json: fix logic when property is not found

src/System.Linq.Dynamic.Core/DynamicClass.cs

@@ -123,6 +123,16 @@ public object? this[string name]
         }
     }
 
+    /// <summary>
+    /// Determines whether a property with the specified name exists in the collection.
+    /// </summary>
+    /// <param name="name">The name of the property to locate. Cannot be null.</param>
+    /// <returns><c>true</c> if a property with the specified name exists; otherwise, <c>false</c>.</returns>
+    public bool ContainsProperty(string name)
+    {
+        return Properties.ContainsKey(name);
+    }
+
     /// <summary>
     /// Returns the enumeration of all dynamic member names.
     /// </summary>

src/System.Linq.Dynamic.Core/DynamicClass.uap.cs

@@ -12,7 +12,7 @@ public class DynamicClass : DynamicObject
 {
     internal const string IndexerName = "System_Linq_Dynamic_Core_DynamicClass_Indexer";
 
-    private readonly Dictionary<string, object> _properties = new();
+    private readonly Dictionary<string, object?> _properties = new();
 
     /// <summary>
     /// Initializes a new instance of the <see cref="DynamicClass"/> class.
@@ -35,7 +35,7 @@ public DynamicClass(params KeyValuePair<string, object>[] propertylist)
     /// <param name="name">The name.</param>
     /// <returns>Value from the property.</returns>
     [IndexerName(IndexerName)]
-    public object this[string name]
+    public object? this[string name]
     {
         get
         {
@@ -59,6 +59,16 @@ public object this[string name]
         }
     }
 
+    /// <summary>
+    /// Determines whether a property with the specified name exists in the collection.
+    /// </summary>
+    /// <param name="name">The name of the property to locate. Cannot be null.</param>
+    /// <returns><c>true</c> if a property with the specified name exists; otherwise, <c>false</c>.</returns>
+    public bool ContainsProperty(string name)
+    {
+        return _properties.ContainsKey(name);
+    }
+
     /// <summary>
     /// Returns the enumeration of all dynamic member names.
     /// </summary>

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

@@ -11,6 +11,7 @@ namespace System.Linq.Dynamic.Core.Parser;
 
 internal class ExpressionHelper : IExpressionHelper
 {
+    private static readonly Expression _nullExpression = Expression.Constant(null);
     private readonly IConstantExpressionWrapper _constantExpressionWrapper = new ConstantExpressionWrapper();
     private readonly ParsingConfig _parsingConfig;
 
@@ -340,7 +341,7 @@ public bool TryGenerateAndAlsoNotNullExpression(Expression sourceExpression, boo
         // Convert all expressions into '!= null' expressions (only if the type can be null)
         var binaryExpressions = expressions
             .Where(expression => TypeHelper.TypeCanBeNull(expression.Type))
-            .Select(expression => Expression.NotEqual(expression, Expression.Constant(null)))
+            .Select(expression => Expression.NotEqual(expression, _nullExpression))
             .ToArray();
 
         // Convert all binary expressions into `AndAlso(...)`
@@ -393,16 +394,46 @@ public bool TryConvertTypes(ref Expression left, ref Expression right)
 
         if (left.Type == typeof(object))
         {
+            if (TryGetAsIndexerExpression(left, out var ce))
+            {
+                var rightTypeAsNullableType = TypeHelper.GetNullableType(right.Type);
+
+                right = Expression.Convert(right, rightTypeAsNullableType);
+
+                left = Expression.Condition(
+                    ce.Test,
+                    Expression.Convert(ce.IfTrue, rightTypeAsNullableType),
+                    Expression.Convert(_nullExpression, rightTypeAsNullableType)
+                );
+
+                return true;
+            }
+
             left = Expression.Condition(
-                Expression.Equal(left, Expression.Constant(null, typeof(object))),
+                Expression.Equal(left, _nullExpression),
                 GenerateDefaultExpression(right.Type),
                 Expression.Convert(left, right.Type)
             );
         }
         else if (right.Type == typeof(object))
         {
+            if (TryGetAsIndexerExpression(right, out var ce))
+            {
+                var leftTypeAsNullableType = TypeHelper.GetNullableType(left.Type);
+
+                left = Expression.Convert(left, leftTypeAsNullableType);
+
+                right = Expression.Condition(
+                    ce.Test,
+                    Expression.Convert(ce.IfTrue, leftTypeAsNullableType),
+                    Expression.Convert(_nullExpression, leftTypeAsNullableType)
+                );
+
+                return true;
+            }
+
             right = Expression.Condition(
-                Expression.Equal(right, Expression.Constant(null, typeof(object))),
+                Expression.Equal(right, _nullExpression),
                 GenerateDefaultExpression(left.Type),
                 Expression.Convert(right, left.Type)
             );
@@ -546,4 +577,17 @@ private static object[] ConvertIfIEnumerableHasValues(IEnumerable? input)
 
         return [];
     }
+
+    private static bool TryGetAsIndexerExpression(Expression expression, [NotNullWhen(true)] out ConditionalExpression? indexerExpresion)
+    {
+        indexerExpresion = expression as ConditionalExpression;
+        if (indexerExpresion == null)
+        {
+            return false;
+        }
+
+        return
+            indexerExpresion.IfTrue.ToString().Contains(DynamicClass.IndexerName) &&
+            indexerExpresion.Test.ToString().Contains("ContainsProperty");
+    }
 }

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

@@ -1921,11 +1921,35 @@
 
         if (!_parsingConfig.DisableMemberAccessToIndexAccessorFallback && extraCheck)
         {
-            var indexerName = TypeHelper.IsDynamicClass(type!) ? DynamicClass.IndexerName : "Item";
+            var isDynamicClass = TypeHelper.IsDynamicClass(type!);
+            var indexerName = isDynamicClass ? DynamicClass.IndexerName : "Item";
+
+            // Try to get the indexer property "Item" or "DynamicClass_Indexer" which takes a string as parameter
             var indexerMethod = expression?.Type.GetMethod($"get_{indexerName}", [typeof(string)]);
             if (indexerMethod != null)
             {
-                return Expression.Call(expression, indexerMethod, Expression.Constant(id));
+                if (!isDynamicClass)
+                {
+                    return Expression.Call(expression, indexerMethod, Expression.Constant(id));
+                }
+
+                var containsPropertyMethod = typeof(DynamicClass).GetMethod("ContainsProperty");
+                if (containsPropertyMethod == null)
+                {
+                    return Expression.Call(expression, indexerMethod, Expression.Constant(id));
+                }
+
+                var callContainsPropertyExpression = Expression.Call(
+                    expression!,
+                    containsPropertyMethod,
+                    Expression.Constant(id)
+                );
+
+                return Expression.Condition(
+                    Expression.Equal(callContainsPropertyExpression, Expression.Constant(true)),
+                    Expression.Call(expression, indexerMethod, Expression.Constant(id)),
+                    Expression.Constant(null)
+                );
             }
         }
 
@@ -1956,7 +1980,7 @@
         switch (member)
         {
             case PropertyInfo property:
                 var propertyIsStatic = property?.GetGetMethod().IsStatic ?? property?.GetSetMethod().IsStatic ?? false;
                 propertyOrFieldExpression = propertyIsStatic ? Expression.Property(null, property) : Expression.Property(expression, property);
                 return true;
 

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

@@ -517,12 +517,14 @@ public void Where_With_Select()
     [InlineData("notExisting == \"1\"")]
     [InlineData("notExisting == \"something\"")]
     [InlineData("notExisting > 1")]
+    [InlineData("notExisting < 1")]
     [InlineData("true == notExisting")]
     [InlineData("\"true\" == notExisting")]
     [InlineData("1 == notExisting")]
     [InlineData("\"1\" == notExisting")]
     [InlineData("\"something\" == notExisting")]
     [InlineData("1 < notExisting")]
+    [InlineData("1 > notExisting")]
     public void Where_NonExistingMember_EmptyResult(string predicate)
     {
         // Arrange

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

@@ -546,12 +546,14 @@ public void Where_With_Select()
     [InlineData("notExisting == \"1\"")]
     [InlineData("notExisting == \"something\"")]
     [InlineData("notExisting > 1")]
+    [InlineData("notExisting < 1")]
     [InlineData("true == notExisting")]
     [InlineData("\"true\" == notExisting")]
     [InlineData("1 == notExisting")]
     [InlineData("\"1\" == notExisting")]
     [InlineData("\"something\" == notExisting")]
     [InlineData("1 < notExisting")]
+    [InlineData("1 > notExisting")]
     public void Where_NonExistingMember_EmptyResult(string predicate)
     {
         // Act