Fixed null-ref for case-(in)sensitive null-search (#165)

* Fixed null-ref for case-insensitive null-search
Added null-escaping sequence (to distinguish between prop==null (as null) and prop==\null (as string))

* Added null-search case-insensitive test

* Code style

* Added escape-sequences description to README.md

Co-authored-by: Nikita Prokhorov <nikita.prokhorov@grse.de>

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,38 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Desktop (please complete the following information):**
+ - OS: [e.g. iOS]
+ - Browser [e.g. chrome, safari]
+ - Version [e.g. 22]
+
+**Smartphone (please complete the following information):**
+ - Device: [e.g. iPhone6]
+ - OS: [e.g. iOS8.1]
+ - Browser [e.g. stock browser, safari]
+ - Version [e.g. 22]
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,5 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Feature Request
+    url: https://github.com/biarity/sieve/discussions/new
+    about: Share your ideas on how to make Sieve better.

.github/workflows/ci_publish.yml

@@ -20,6 +20,8 @@ on:
   push:
     branches:
       - 'releases/*'
+    tags:
+      - 'v*'
 
 jobs:
   ubuntu-latest:

README.md

@@ -2,7 +2,8 @@
 ⚗️ Sieve is a simple, clean, and extensible framework for .NET Core that **adds sorting, filtering, and pagination functionality out of the box**. 
 Most common use case would be for serving ASP.NET Core GET queries.
 
-[![NuGet Release](https://img.shields.io/nuget/v/Sieve.svg?style=flat-square)](https://www.nuget.org/packages/Sieve)
+[![NuGet Release](https://img.shields.io/nuget/v/Sieve?style=for-the-badge)](https://www.nuget.org/packages/Sieve)
+[![NuGet Pre-Release](https://img.shields.io/nuget/vpre/Sieve?style=for-the-badge)](https://www.nuget.org/packages/Sieve)
 
 [Get Sieve on nuget](https://www.nuget.org/packages/Sieve/)
 
@@ -74,7 +75,7 @@ Where `SieveCustomSortMethodsOfPosts` for example is:
 ```C#
 public class SieveCustomSortMethods : ISieveCustomSortMethods
 {
-    public IQueryable<Post> Popularity(IQueryable<Post> source, bool useThenBy, bool desc) // The method is given an indicator of weather to use ThenBy(), and if the query is descending 
+    public IQueryable<Post> Popularity(IQueryable<Post> source, bool useThenBy, bool desc) // The method is given an indicator of whether to use ThenBy(), and if the query is descending 
     {
         var result = useThenBy ?
             ((IOrderedQueryable<Post>)source).ThenBy(p => p.LikeCount) : // ThenBy only works on IOrderedQueryable<TEntity>
@@ -127,7 +128,8 @@ Then you can add the configuration:
         "CaseSensitive": "boolean: should property names be case-sensitive? Defaults to false",
         "DefaultPageSize": "int number: optional number to fallback to when no page argument is given. Set <=0 to disable paging if no pageSize is specified (default).",
         "MaxPageSize": "int number: maximum allowed page size. Set <=0 to make infinite (default)",
-        "ThrowExceptions": "boolean: should Sieve throw exceptions instead of silently failing? Defaults to false"
+        "ThrowExceptions": "boolean: should Sieve throw exceptions instead of silently failing? Defaults to false",
+        "IgnoreNullsOnNotEqual": "boolean: ignore null values when filtering using is not equal operator? Default to true"
     }
 }
 ```
@@ -157,7 +159,10 @@ More formally:
 * `pageSize` is the number of items returned per page 
 
 Notes:
-* You can use backslashes to escape commas and pipes within value fields
+* You can use backslashes to escape special characters and sequences:
+    * commas: `Title@=some\,title` makes a match with "some,title"
+    * pipes: `Title@=some\|title` makes a match with "some|title"
+    * null values: `Title@=\null` will search for items with title equal to "null" (not a missing value, but "null"-string literally)
 * You can have spaces anywhere except *within* `{Name}` or `{Operator}` fields
 * If you need to look at the data before applying pagination (eg. get total count), use the optional paramters on `Apply` to defer pagination (an [example](https://github.com/Biarity/Sieve/issues/34))
 * Here's a [good example on how to work with enumerables](https://github.com/Biarity/Sieve/issues/2)

Sieve.Sample/appsettings.Development.json

@@ -1,6 +1,5 @@
 {
   "Logging": {
-    "IncludeScopes": false,
     "LogLevel": {
       "Default": "Debug",
       "System": "Information",

Sieve.Sample/appsettings.json

@@ -4,10 +4,10 @@
   },
   "Sieve": {
     "CaseSensitive": false,
-    "DefaultPageSize": 10
+    "DefaultPageSize": 10,
+    "IgnoreNullsOnNotEqual": true
   },
   "Logging": {
-    "IncludeScopes": false,
     "Debug": {
       "LogLevel": {
         "Default": "Warning"

Sieve/Models/FilterTerm.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Text.RegularExpressions;
 
@@ -6,45 +7,49 @@ namespace Sieve.Models
 {
     public class FilterTerm : IFilterTerm, IEquatable<FilterTerm>
     {
-        public FilterTerm() { }
+        private const string EscapedPipePattern = @"(?<!($|[^\\]|^)(\\\\)*?\\)\|";
+        private const string OperatorsRegEx = @"(!@=\*|!_=\*|!=\*|!@=|!_=|==\*|@=\*|_=\*|==|!=|>=|<=|>|<|@=|_=)";
+        private const string EscapeNegPatternForOper = @"(?<!\\)" + OperatorsRegEx;
+        private const string EscapePosPatternForOper = @"(?<=\\)" + OperatorsRegEx;
 
-        private const string EscapedPipePattern = @"(?<!($|[^\\])(\\\\)*?\\)\|";
-
-        private static readonly string[] Operators = new string[] {
-                    "!@=*",
-                    "!_=*",
-                    "!=*",
-                    "!@=",
-                    "!_=",
-                    "==*",
-                    "@=*",
-                    "_=*",
-                    "==",
-                    "!=",
-                    ">=",
-                    "<=",
-                    ">",
-                    "<",
-                    "@=",
-                    "_="
+        private static readonly HashSet<string> _escapedSequences = new HashSet<string>
+        {
+            @"\|",
+            @"\\"
         };
 
         public string Filter
         {
             set
             {
-                var filterSplits = value.Split(Operators, StringSplitOptions.RemoveEmptyEntries)
-                    .Select(t => t.Trim()).ToArray();
+                var filterSplits = Regex.Split(value,EscapeNegPatternForOper).Select(t => t.Trim()).ToArray();
+                
                 Names = Regex.Split(filterSplits[0], EscapedPipePattern).Select(t => t.Trim()).ToArray();
-                Values = filterSplits.Length > 1 ? Regex.Split(filterSplits[1], EscapedPipePattern).Select(t => t.Trim()).ToArray() : null;
-                Operator = Array.Find(Operators, o => value.Contains(o)) ?? "==";
+
+                if (filterSplits.Length > 2)
+                {
+                    foreach (var match in Regex.Matches(filterSplits[2],EscapePosPatternForOper))
+                    {
+                        var matchStr = match.ToString();
+                        filterSplits[2] = filterSplits[2].Replace('\\' + matchStr, matchStr);
+                    }
+
+                    Values = Regex.Split(filterSplits[2], EscapedPipePattern)
+                        .Select(UnEscape)
+                        .ToArray();
+                }
+ 
+                Operator = Regex.Match(value,EscapeNegPatternForOper).Value;
                 OperatorParsed = GetOperatorParsed(Operator);
                 OperatorIsCaseInsensitive = Operator.EndsWith("*");
                 OperatorIsNegated = OperatorParsed != FilterOperator.NotEquals && Operator.StartsWith("!");
             }
-
         }
 
+        private string UnEscape(string escapedTerm)
+            => _escapedSequences.Aggregate(escapedTerm,
+                (current, sequence) => Regex.Replace(current, $@"(\\)({sequence})", "$2"));
+
         public string[] Names { get; private set; }
 
         public FilterOperator OperatorParsed { get; private set; }
@@ -90,6 +95,5 @@ namespace Sieve.Models
                 && Values.SequenceEqual(other.Values)
                 && Operator == other.Operator;
         }
-
     }
 }

Sieve/Models/SieveModel.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using System.Linq;

Sieve/Models/SieveOptions.cs

@@ -2,27 +2,14 @@
 {
     public class SieveOptions
     {
-        /// <summary>
-        /// If flag is set, property names have to match including case sensitivity.
-        /// </summary>
         public bool CaseSensitive { get; set; } = false;
 
-        /// <summary>
-        /// Fallback value of no page size is specified in the request.
-        /// </summary>
-        /// <remarks>Values less or equal to 0 disable paging.</remarks>
         public int DefaultPageSize { get; set; } = 0;
 
-        /// <summary>
-        /// Specifies the upper limit of a page size to be requested.
-        /// </summary>
-        /// <remarks>Values less or equal to 0 are ignored.</remarks>
         public int MaxPageSize { get; set; } = 0;
 
-        /// <summary>
-        /// If flag is set, Sieve throws exception otherwise exceptions are caught and the already processed
-        /// result is returned.
-        /// </summary>
-        public bool ThrowExceptions { get; set; } = true;
+        public bool ThrowExceptions { get; set; } = false;
+
+        public bool IgnoreNullsOnNotEqual { get; set; } = true;
     }
 }

Sieve/Services/SieveProcessor.cs

@@ -68,7 +68,7 @@ namespace Sieve.Services
         where TSortTerm : ISortTerm, new()
     {
         private const string NullFilterValue = "null";
-        private readonly IOptions<SieveOptions> _options;
+        private const char EscapeChar = '\\';
         private readonly ISieveCustomSortMethods _customSortMethods;
         private readonly ISieveCustomFilterMethods _customFilterMethods;
         private readonly SievePropertyMapper _mapper = new SievePropertyMapper();
@@ -78,7 +78,7 @@ namespace Sieve.Services
             ISieveCustomFilterMethods customFilterMethods)
         {
             _mapper = MapProperties(_mapper);
-            _options = options;
+            Options = options;
             _customSortMethods = customSortMethods;
             _customFilterMethods = customFilterMethods;
         }
@@ -87,7 +87,7 @@ namespace Sieve.Services
             ISieveCustomSortMethods customSortMethods)
         {
             _mapper = MapProperties(_mapper);
-            _options = options;
+            Options = options;
             _customSortMethods = customSortMethods;
         }
 
@@ -95,16 +95,18 @@ namespace Sieve.Services
             ISieveCustomFilterMethods customFilterMethods)
         {
             _mapper = MapProperties(_mapper);
-            _options = options;
+            Options = options;
             _customFilterMethods = customFilterMethods;
         }
 
         public SieveProcessor(IOptions<SieveOptions> options)
         {
             _mapper = MapProperties(_mapper);
-            _options = options;
+            Options = options;
         }
 
+        protected IOptions<SieveOptions> Options { get; }
+
         /// <summary>
         /// Apply filtering, sorting, and pagination parameters found in `model` to `source`
         /// </summary>
@@ -148,7 +150,7 @@ namespace Sieve.Services
             }
             catch (Exception ex)
             {
-                if (!_options.Value.ThrowExceptions)
+                if (!Options.Value.ThrowExceptions)
                 {
                     return result;
                 }
@@ -162,7 +164,7 @@ namespace Sieve.Services
             }
         }
 
-        private IQueryable<TEntity> ApplyFiltering<TEntity>(TSieveModel model, IQueryable<TEntity> result,
+        protected virtual IQueryable<TEntity> ApplyFiltering<TEntity>(TSieveModel model, IQueryable<TEntity> result,
             object[] dataForCustomMethods = null)
         {
             if (model?.GetFiltersParsed() == null)
@@ -198,7 +200,7 @@ namespace Sieve.Services
                                 ? Expression.Constant(null, property.PropertyType)
                                 : ConvertStringValueToConstantExpression(filterTermValue, property, converter);
 
-                            if (filterTerm.OperatorIsCaseInsensitive)
+                            if (filterTerm.OperatorIsCaseInsensitive && !isFilterTermValueNull)
                             {
                                 propertyValue = Expression.Call(propertyValue,
                                     typeof(string).GetMethods()
@@ -216,10 +218,13 @@ namespace Sieve.Services
                                 expression = Expression.Not(expression);
                             }
 
-                            var filterValueNullCheck = GetFilterValueNullCheck(parameter, fullPropertyName, isFilterTermValueNull);
-                            if (filterValueNullCheck != null)
+                            if (expression.NodeType != ExpressionType.NotEqual || Options.Value.IgnoreNullsOnNotEqual)
                             {
-                                expression = Expression.AndAlso(filterValueNullCheck, expression);
+                                var filterValueNullCheck = GetFilterValueNullCheck(parameter, fullPropertyName, isFilterTermValueNull);
+                                if (filterValueNullCheck != null)
+                                {
+                                    expression = Expression.AndAlso(filterValueNullCheck, expression);
+                                }
                             }
 
                             innerExpression = innerExpression == null
@@ -253,8 +258,7 @@ namespace Sieve.Services
                 : result.Where(Expression.Lambda<Func<TEntity, bool>>(outerExpression, parameter));
         }
 
-        private static Expression GetFilterValueNullCheck(Expression parameter, string fullPropertyName,
-            bool isFilterTermValueNull)
+        private static Expression GetFilterValueNullCheck(Expression parameter, string fullPropertyName, bool isFilterTermValueNull)
         {
             var (propertyValue, nullCheck) = GetPropertyValueAndNullCheckExpression(parameter, fullPropertyName);
 
@@ -308,6 +312,10 @@ namespace Sieve.Services
         private static Expression ConvertStringValueToConstantExpression(string value, PropertyInfo property,
             TypeConverter converter)
         {
+            // to allow user to distinguish between prop==null (as null) and prop==\null (as "null"-string)
+            value = value.Equals(EscapeChar + NullFilterValue, StringComparison.InvariantCultureIgnoreCase) 
+                ? value.TrimStart(EscapeChar) 
+                : value;
             dynamic constantVal = converter.CanConvertFrom(typeof(string))
                 ? converter.ConvertFrom(value)
                 : Convert.ChangeType(value, property.PropertyType);
@@ -336,15 +344,13 @@ namespace Sieve.Services
         }
 
         // Workaround to ensure that the filter value gets passed as a parameter in generated SQL from EF Core
-        // See https://github.com/aspnet/EntityFrameworkCore/issues/3361
-        // Expression.Constant passed the target type to allow Nullable comparison
-        // See http://bradwilson.typepad.com/blog/2008/07/creating-nullab.html
         private static Expression GetClosureOverConstant<T>(T constant, Type targetType)
         {
-            return Expression.Constant(constant, targetType);
+            Expression<Func<T>> hoistedConstant = () => constant;
+            return Expression.Convert(hoistedConstant.Body, targetType);
         }
 
-        private IQueryable<TEntity> ApplySorting<TEntity>(TSieveModel model, IQueryable<TEntity> result,
+        protected virtual IQueryable<TEntity> ApplySorting<TEntity>(TSieveModel model, IQueryable<TEntity> result,
             object[] dataForCustomMethods = null)
         {
             if (model?.GetSortsParsed() == null)
@@ -373,15 +379,11 @@ namespace Sieve.Services
             return result;
         }
 
-        private IQueryable<TEntity> ApplyPagination<TEntity>(TSieveModel model, IQueryable<TEntity> result)
+        protected virtual IQueryable<TEntity> ApplyPagination<TEntity>(TSieveModel model, IQueryable<TEntity> result)
         {
             var page = model?.Page ?? 1;
-            var pageSize = model?.PageSize ?? _options.Value.DefaultPageSize;
-
-            if (_options.Value.MaxPageSize > 0)
-            {
-                pageSize = Math.Min(pageSize, _options.Value.MaxPageSize);
-            }
+            var pageSize = model?.PageSize ?? Options.Value.DefaultPageSize;
+            var maxPageSize = Options.Value.MaxPageSize > 0 ? Options.Value.MaxPageSize : pageSize;
 
             if (pageSize <= 0)
             {
@@ -389,7 +391,7 @@ namespace Sieve.Services
             }
 
             result = result.Skip((page - 1) * pageSize);
-            result = result.Take(pageSize);
+            result = result.Take(Math.Min(pageSize, maxPageSize));
 
             return result;
         }
@@ -403,14 +405,14 @@ namespace Sieve.Services
             string name)
         {
             var property = _mapper.FindProperty<TEntity>(canSortRequired, canFilterRequired, name,
-                _options.Value.CaseSensitive);
+                Options.Value.CaseSensitive);
             if (property.Item1 != null)
             {
                 return property;
             }
 
             var prop = FindPropertyBySieveAttribute<TEntity>(canSortRequired, canFilterRequired, name,
-                _options.Value.CaseSensitive);
+                Options.Value.CaseSensitive);
             return (prop?.Name, prop);
         }
 
@@ -430,7 +432,7 @@ namespace Sieve.Services
         {
             var customMethod = parent?.GetType()
                 .GetMethodExt(name,
-                    _options.Value.CaseSensitive
+                    Options.Value.CaseSensitive
                         ? BindingFlags.Default
                         : BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance,
                     typeof(IQueryable<TEntity>));
@@ -441,7 +443,7 @@ namespace Sieve.Services
                 // Find generic methods `public IQueryable<T> Filter<T>(IQueryable<T> source, ...)`
                 var genericCustomMethod = parent?.GetType()
                     .GetMethodExt(name,
-                        _options.Value.CaseSensitive
+                        Options.Value.CaseSensitive
                             ? BindingFlags.Default
                             : BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance,
                         typeof(IQueryable<>));
@@ -485,11 +487,11 @@ namespace Sieve.Services
                 var incompatibleCustomMethods =
                     parent?
                         .GetType()
-                        .GetMethods(_options.Value.CaseSensitive
+                        .GetMethods(Options.Value.CaseSensitive
                             ? BindingFlags.Default
                             : BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance)
                         .Where(method => string.Equals(method.Name, name,
-                            _options.Value.CaseSensitive
+                            Options.Value.CaseSensitive
                                 ? StringComparison.InvariantCulture
                                 : StringComparison.InvariantCultureIgnoreCase))
                         .ToList()

SieveUnitTests/General.cs

@@ -15,16 +15,24 @@ namespace SieveUnitTests
     {
         private readonly ITestOutputHelper _testOutputHelper;
         private readonly SieveProcessor _processor;
+        private readonly SieveProcessor _nullableProcessor;
         private readonly IQueryable<Post> _posts;
         private readonly IQueryable<Comment> _comments;
 
         public General(ITestOutputHelper testOutputHelper)
         {
+            var nullableAccessor = new SieveOptionsAccessor();
+            nullableAccessor.Value.IgnoreNullsOnNotEqual = false;
+
             _testOutputHelper = testOutputHelper;
             _processor = new ApplicationSieveProcessor(new SieveOptionsAccessor(),
                 new SieveCustomSortMethods(),
                 new SieveCustomFilterMethods());
 
+            _nullableProcessor = new ApplicationSieveProcessor(nullableAccessor,
+                new SieveCustomSortMethods(),
+                new SieveCustomFilterMethods());
+
             _posts = new List<Post>
             {
                 new Post
@@ -65,7 +73,7 @@ namespace SieveUnitTests
                     CategoryId = 2,
                     TopComment = new Comment { Id = 1, Text = "D1" },
                     FeaturedComment = new Comment { Id = 7, Text = "D2" }
-                },
+                }
             }.AsQueryable();
 
             _comments = new List<Comment>
@@ -180,8 +188,25 @@ namespace SieveUnitTests
             };
 
             var result = _processor.Apply(model, _posts);
+            var nullableResult = _nullableProcessor.Apply(model, _posts);
 
             Assert.True(result.Count() == 2);
+            Assert.True(nullableResult.Count() == 2);
+        }
+
+        [Fact]
+        public void CanFilterNullableIntsWithNotEqual()
+        {
+            var model = new SieveModel()
+            {
+                Filters = "CategoryId!=1"
+            };
+
+            var result = _processor.Apply(model, _posts);
+            var nullableResult = _nullableProcessor.Apply(model, _posts);
+
+            Assert.True(result.Count() == 1);
+            Assert.True(nullableResult.Count() == 2);
         }
 
         [Theory]
@@ -614,43 +639,161 @@ namespace SieveUnitTests
             Assert.Equal(0,posts[3].Id);
         }
 
-        [Theory]
-        [InlineData(1)]
-        [InlineData(2)]
-        [InlineData(3)]
-        [InlineData(4)]
-        public void Paging_DifferentPages(int page)
+        [Fact]
+        public void CanFilter_WithEscapeCharacter()
         {
+            var comments = new List<Comment>
+            {
+                new Comment
+                {
+                    Id = 0,
+                    DateCreated = DateTimeOffset.UtcNow,
+                    Text = "Here is, a comment"
+                },
+                new Comment
+                {
+                    Id = 1,
+                    DateCreated = DateTimeOffset.UtcNow.AddDays(-1),
+                    Text = "Here is, another comment"
+                },
+            }.AsQueryable();
+
             var model = new SieveModel
             {
-                Page = page,
-                PageSize = 1,
+                Filters = "Text==Here is\\, another comment"
             };
 
-            var result = _processor.Apply(model, _posts);
-            var posts = result.ToList();
+            var result = _processor.Apply(model, comments);
+            Assert.Equal(1, result.Count());
+        }
 
-            Assert.Single(posts);
-            var expectedId = page - 1;
-            Assert.Equal(expectedId, posts.First().Id);
+        [Fact]
+        public void OrEscapedPipeValueFilteringWorks()
+        {
+            var comments = new List<Comment>
+            {
+                new Comment
+                {
+                    Id = 0,
+                    DateCreated = DateTimeOffset.UtcNow,
+                    Text = "Here is | a comment"
+                },
+                new Comment
+                {
+                    Id = 1,
+                    DateCreated = DateTimeOffset.UtcNow.AddDays(-1),
+                    Text = "Here is | another comment"
+                },
+                new Comment
+                {
+                    Id = 2,
+                    DateCreated = DateTimeOffset.UtcNow.AddDays(-1),
+                    Text = @"Here is \| another comment(1)"
+                }
+            }.AsQueryable();
+
+            var model = new SieveModel
+            {
+                Filters = @"Text==Here is \| a comment|Here is \| another comment|Here is \\\| another comment(1)",
+            };
+
+            var result = _processor.Apply(model, comments);
+            Assert.Equal(3, result.Count());
         }
         
         [Theory]
-        [InlineData(1)]
-        [InlineData(2)]
-        [InlineData(3)]
-        [InlineData(4)]
-        public void Paging_DifferentPageSizes(int pageSize)
+        [InlineData("CategoryId==1,(CategoryId|LikeCount)==50")]
+        [InlineData("(CategoryId|LikeCount)==50,CategoryId==1")]
+        public void CanFilterWithEscape(string filter)
         {
             var model = new SieveModel
             {
-                Page = 1,
-                PageSize = pageSize,
+                Filters = filter
             };
 
             var result = _processor.Apply(model, _posts);
+            var entry = result.FirstOrDefault();
+            var resultCount = result.Count();
 
-            Assert.Equal(pageSize, result.Count());
+            Assert.NotNull(entry);
+            Assert.Equal(1, resultCount);
         }
+        
+        [Theory]
+        [InlineData(@"Title@=\\")]
+        public void CanFilterWithEscapedBackSlash(string filter)
+        {
+            var posts = new List<Post>
+            {
+                new Post
+                {
+                    Id = 1,
+                    Title = "E\\",
+                    LikeCount = 4,
+                    IsDraft = true,
+                    CategoryId = 1,
+                    TopComment = new Comment { Id = 1, Text = "E1" },
+                    FeaturedComment = new Comment { Id = 7, Text = "E2" }
+                }
+            }.AsQueryable();
+            
+            var model = new SieveModel
+            {
+                Filters = filter
+            };
+
+            var result = _processor.Apply(model, posts);
+            var entry = result.FirstOrDefault();
+            var resultCount = result.Count();
+
+            Assert.NotNull(entry);
+            Assert.Equal(1, resultCount);
+        }
+        
+        [Theory]
+        [InlineData(@"Title@=\== ")]
+        [InlineData(@"Title@=\!= ")]
+        [InlineData(@"Title@=\> ")]
+        [InlineData(@"Title@=\< ")]
+        [InlineData(@"Title@=\<= ")]
+        [InlineData(@"Title@=\>= ")]
+        [InlineData(@"Title@=\@= ")]
+        [InlineData(@"Title@=\_= ")]
+        [InlineData(@"Title@=!\@= ")]
+        [InlineData(@"Title@=!\_= ")]
+        [InlineData(@"Title@=\@=* ")]
+        [InlineData(@"Title@=\_=* ")]
+        [InlineData(@"Title@=\==* ")]
+        [InlineData(@"Title@=\!=* ")]
+        [InlineData(@"Title@=!\@=* ")]
+        public void CanFilterWithEscapedOperators(string filter)
+        {
+            var posts = new List<Post>
+            {
+                new Post
+                {
+                    Id = 1,
+                    Title = @"Operators: == != > < >= <= @= _= !@= !_= @=* _=* ==* !=* !@=* !_=* ",
+                    LikeCount = 1,
+                    IsDraft = true,
+                    CategoryId = 1,
+                    TopComment = new Comment { Id = 1, Text = "F1" },
+                    FeaturedComment = new Comment { Id = 7, Text = "F2" }
+                }
+            }.AsQueryable();
+            
+            var model = new SieveModel
+            {
+                Filters = filter,
+            };
+
+            var result = _processor.Apply(model, posts);
+            var entry = result.FirstOrDefault();
+            var resultCount = result.Count();
+
+            Assert.NotNull(entry);
+            Assert.Equal(1, resultCount);
+        }
+        
     }
 }

SieveUnitTests/GeneralWithInterfaces.cs

@@ -16,16 +16,24 @@ namespace SieveUnitTests
     {
         private readonly ITestOutputHelper _testOutputHelper;
         private readonly SieveProcessor _processor;
+        private readonly SieveProcessor _nullableProcessor;
         private readonly IQueryable<IPost> _posts;
         private readonly IQueryable<Comment> _comments;
 
         public GeneralWithInterfaces(ITestOutputHelper testOutputHelper)
         {
+            var nullableAccessor = new SieveOptionsAccessor();
+            nullableAccessor.Value.IgnoreNullsOnNotEqual = false;
+
             _testOutputHelper = testOutputHelper;
             _processor = new ApplicationSieveProcessor(new SieveOptionsAccessor(),
                 new SieveCustomSortMethods(),
                 new SieveCustomFilterMethods());
 
+            _nullableProcessor = new ApplicationSieveProcessor(nullableAccessor,
+                new SieveCustomSortMethods(),
+                new SieveCustomFilterMethods());
+
             _posts = new List<IPost>
             {
                 new Post
@@ -181,8 +189,25 @@ namespace SieveUnitTests
             };
 
             var result = _processor.Apply(model, _posts);
+            var nullableResult = _nullableProcessor.Apply(model, _posts);
 
             Assert.True(result.Count() == 2);
+            Assert.True(nullableResult.Count() == 2);
+        }
+
+        [Fact]
+        public void CanFilterNullableIntsWithNotEqual()
+        {
+            var model = new SieveModel()
+            {
+                Filters = "CategoryId!=1"
+            };
+
+            var result = _processor.Apply(model, _posts);
+            var nullableResult = _nullableProcessor.Apply(model, _posts);
+
+            Assert.True(result.Count() == 1);
+            Assert.True(nullableResult.Count() == 2);
         }
 
         [Fact]

SieveUnitTests/StringFilterNullTests.cs

@@ -38,7 +38,7 @@ namespace SieveUnitTests
                 {
                     Id = 2, 
                     DateCreated = DateTimeOffset.UtcNow, 
-                    Text = "Regular comment without n*ll.",
+                    Text = "Regular comment without n*ll",
                     Author = "Mouse",
                 },
                 new Comment
@@ -47,24 +47,28 @@ namespace SieveUnitTests
                     DateCreated = DateTimeOffset.UtcNow, 
                     Text = null,
                     Author = "null",
-                },
+                }
             }.AsQueryable();
         }
 
-        [Fact]
-        public void Filter_Equals_Null()
+        [Theory]
+        [InlineData("Text==null")]
+        [InlineData("Text==*null")]
+        public void Filter_Equals_Null(string filter)
         {
-            var model = new SieveModel {Filters = "Text==null"};
+            var model = new SieveModel {Filters = filter};
 
             var result = _processor.Apply(model, _comments);
 
             Assert.Equal(100, result.Single().Id);
         }
 
-        [Fact]
-        public void Filter_NotEquals_Null()
+        [Theory]
+        [InlineData("Text!=null")]
+        [InlineData("Text!=*null")]
+        public void Filter_NotEquals_Null(string filter)
         {
-            var model = new SieveModel {Filters = "Text!=null"};
+            var model = new SieveModel {Filters = filter};
 
             var result = _processor.Apply(model, _comments);
 
@@ -101,6 +105,22 @@ namespace SieveUnitTests
             Assert.Equal(expectedIds, result.Select(p => p.Id));
         }
 
+        [Theory]
+        [InlineData(@"Author==\null", 100)]
+        [InlineData(@"Author==*\null", 100)]
+        [InlineData(@"Author==*\NuLl", 100)]
+        [InlineData(@"Author!=*\null", 0, 1, 2)]
+        [InlineData(@"Author!=*\NulL", 0, 1, 2)]
+        [InlineData(@"Author!=\null", 0, 1, 2)]
+        public void SingleFilter_Equals_NullStringEscaped(string filter, params int[] expectedIds)
+        {
+            var model = new SieveModel {Filters = filter};
+
+            var result = _processor.Apply(model, _comments);
+
+            Assert.Equal(expectedIds, result.Select(p => p.Id));
+        }
+
         [Theory]
         [InlineData("Text_=null")]
         [InlineData("Text_=*null")]

build/Build.cs

@@ -21,7 +21,8 @@ using static Nuke.Common.Tools.DotNet.DotNetTasks;
     InvokedTargets = new[] {nameof(Ci)},
     CacheKeyFiles = new string[0])]
 [GitHubActions("ci_publish", GitHubActionsImage.UbuntuLatest,
-    OnPushBranches = new[] {"releases/*"},
+    OnPushBranches = new[] { "releases/*" },
+    OnPushTags = new[] { "v*" },
     AutoGenerate = true,
     InvokedTargets = new[] {nameof(CiPublish)},
     CacheKeyFiles = new string[0],
@@ -83,6 +84,7 @@ class Build : NukeBuild
     Target Package => _ => _
         .DependsOn(Test)
         .Executes(() =>
+        
         {
             DotNetPack(s => s
                 .SetProject(SieveProject)