Fix ExpressionHelper.TryConvertTypes to generate correct Convert in case left or right is null

src/System.Linq.Dynamic.Core.NewtonsoftJson/NewtonsoftJsonExtensions.cs

@@ -821,7 +821,7 @@ public static JArray Where(this JArray source, NewtonsoftJsonParsingConfig confi
 
         if (source.Count == 0)
         {
-            return new JArray();
+            return [];
         }
 
         var queryable = ToQueryable(source, config);
@@ -848,7 +848,8 @@ public static JArray Where(this JArray source, NewtonsoftJsonParsingConfig confi
     private static JArray ToJArray(Func<IQueryable> func)
     {
         var array = new JArray();
-        foreach (var dynamicElement in func())
+        var funcResult = func();
+        foreach (var dynamicElement in funcResult)
         {
             var element = dynamicElement switch
             {

src/System.Linq.Dynamic.Core/Parser/ExpressionHelper.cs

@@ -361,7 +361,12 @@ public bool ExpressionQualifiesForNullPropagation(Expression? expression)
     public Expression GenerateDefaultExpression(Type type)
     {
 #if NET35
-        return Expression.Constant(Activator.CreateInstance(type));
+        if (type.IsValueType)
+        {
+            return Expression.Constant(Activator.CreateInstance(type), type);
+        }
+
+        return Expression.Constant(null, type);
 #else
         return Expression.Default(type);
 #endif
@@ -388,11 +393,19 @@ public bool TryConvertTypes(ref Expression left, ref Expression right)
 
         if (left.Type == typeof(object))
         {
-            left = Expression.Convert(left, right.Type);
+            left = Expression.Condition(
+                Expression.Equal(left, Expression.Constant(null, typeof(object))),
+                GenerateDefaultExpression(right.Type),
+                Expression.Convert(left, right.Type)
+            );
         }
         else if (right.Type == typeof(object))
         {
-            right = Expression.Convert(right, left.Type);
+            right = Expression.Condition(
+                Expression.Equal(right, Expression.Constant(null, typeof(object))),
+                GenerateDefaultExpression(left.Type),
+                Expression.Convert(right, left.Type)
+            );
         }
 
         return true;

src/System.Linq.Dynamic.Core/Parser/IExpressionHelper.cs

@@ -52,5 +52,5 @@ internal interface IExpressionHelper
     /// <summary>
     /// If the types are different (and not null), try to convert the object type to other type.
     /// </summary>
-    public bool TryConvertTypes(ref Expression left, ref Expression right);
+    bool TryConvertTypes(ref Expression left, ref Expression right);
 }

test/System.Linq.Dynamic.Core.NewtonsoftJson.Tests/NewtonsoftJsonTests.cs

@@ -1,4 +1,5 @@
-using FluentAssertions;
+using System.Linq.Dynamic.Core.NewtonsoftJson.Config;
+using FluentAssertions;
 using Newtonsoft.Json.Linq;
 using Xunit;
 
@@ -506,4 +507,62 @@ public void Where_With_Select()
         var first = result.First();
         first.Value<string>().Should().Be("Doe");
     }
+
+    //[Fact]
+    //public void Where_OptionalProperty()
+    //{
+    //    // Arrange
+    //    var config = new NewtonsoftJsonParsingConfig
+    //    {
+    //        ConvertObjectToSupportComparison = true
+    //    };
+    //    var array =
+    //        """
+    //        [
+    //            {
+    //                "Name": "John",
+    //                "Age": 30
+    //            },
+    //            {
+    //                "Name": "Doe"
+    //            }
+    //        ]
+    //        """;
+
+    //    // Act
+    //    var result = JArray.Parse(array).Where(config, "Age > 30").Select("Name");
+
+    //    // Assert
+    //    result.Should().HaveCount(1);
+    //    var first = result.First();
+    //    first.Value<string>().Should().Be("John");
+    //}
+
+    [Theory]
+    [InlineData("notExisting == true")]
+    [InlineData("notExisting == \"true\"")]
+    [InlineData("notExisting == 1")]
+    [InlineData("notExisting == \"1\"")]
+    [InlineData("notExisting == \"something\"")]
+    [InlineData("notExisting > 1")]
+    [InlineData("true == notExisting")]
+    [InlineData("\"true\" == notExisting")]
+    [InlineData("1 == notExisting")]
+    [InlineData("\"1\" == notExisting")]
+    [InlineData("\"something\" == notExisting")]
+    [InlineData("1 < notExisting")]
+    public void Where_NonExistingMember_EmptyResult(string predicate)
+    {
+        // Arrange
+        var config = new NewtonsoftJsonParsingConfig
+        {
+            ConvertObjectToSupportComparison = true
+        };
+
+        // Act
+        var result = _source.Where(config, predicate);
+
+        // Assert
+        result.Should().BeEmpty();
+    }
 }

test/System.Linq.Dynamic.Core.SystemTextJson.Tests/SystemTextJsonTests.cs

@@ -1,4 +1,5 @@
-using System.Text.Json;
+using System.Linq.Dynamic.Core.SystemTextJson.Config;
+using System.Text.Json;
 using FluentAssertions;
 using Xunit;
 
@@ -535,4 +536,32 @@ public void Where_With_Select()
         array.Should().HaveCount(1);
         array.First().GetString().Should().Be("Doe");
     }
+
+    [Theory]
+    [InlineData("notExisting == true")]
+    [InlineData("notExisting == \"true\"")]
+    [InlineData("notExisting == 1")]
+    [InlineData("notExisting == \"1\"")]
+    [InlineData("notExisting == \"something\"")]
+    [InlineData("notExisting > 1")]
+    [InlineData("true == notExisting")]
+    [InlineData("\"true\" == notExisting")]
+    [InlineData("1 == notExisting")]
+    [InlineData("\"1\" == notExisting")]
+    [InlineData("\"something\" == notExisting")]
+    [InlineData("1 < notExisting")]
+    public void Where_NonExistingMember_EmptyResult(string predicate)
+    {
+        // Arrange
+        var config = new SystemTextJsonParsingConfig
+        {
+            ConvertObjectToSupportComparison = true
+        };
+
+        // Act
+        var result = _source.Where(config, predicate).RootElement.EnumerateArray();
+
+        // Assert
+        result.Should().BeEmpty();
+    }
 }

test/System.Linq.Dynamic.Core.Tests/DynamicClassTest.cs

@@ -131,20 +131,24 @@ public void DynamicClass_GettingValue_ByIndex_Should_Work()
     public void DynamicClass_SettingExistingPropertyValue_ByIndex_Should_Work()
     {
         // Arrange
-        var test = "Test";
-        var newTest = "abc";
-        var range = new List<object>
+        var originalValue = "Test";
+        var newValue = "abc";
+        var array = new object[]
         {
-            new { FieldName = test, Value = 3.14159 }
+            new
+            {
+                FieldName = originalValue, 
+                Value = 3.14159
+            }
         };
 
         // Act
-        var rangeResult = range.AsQueryable().Select("new(FieldName as FieldName)").ToDynamicList();
+        var rangeResult = array.AsQueryable().Select("new(FieldName as FieldName)").ToDynamicList();
         var item = rangeResult.First();
 
-        item["FieldName"] = newTest;
+        item["FieldName"] = newValue;
         var value = item["FieldName"] as string;
-        value.Should().Be(newTest);
+        value.Should().Be(newValue);
     }
 
     [Fact]