Null propagation for methods

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

@@ -250,7 +250,7 @@ public bool TryGenerateAndAlsoNotNullExpression(Expression sourceExpression, out
 
             var expressions = CollectExpressions(sourceExpression);
 
-            if (expressions.Count == 1)
+            if (expressions.Count == 1 && !(expressions[0] is MethodCallExpression))
             {
                 generatedExpression = sourceExpression;
                 return false;
@@ -274,14 +274,19 @@ public bool TryGenerateAndAlsoNotNullExpression(Expression sourceExpression, out
 
         private static Expression GetMemberExpression(Expression expression)
         {
+            if (expression is MemberExpression memberExpression)
+            {
+                return memberExpression;
+            }
+
             if (expression is ParameterExpression parameterExpression)
             {
                 return parameterExpression;
             }
 
-            if (expression is MemberExpression memberExpression)
+            if (expression is MethodCallExpression methodCallExpression)
             {
-                return memberExpression;
+                return methodCallExpression;
             }
 
             if (expression is LambdaExpression lambdaExpression)
@@ -291,9 +296,9 @@ private static Expression GetMemberExpression(Expression expression)
                     return bodyAsMemberExpression;
                 }
 
-                if (lambdaExpression.Body is UnaryExpression bodyAsunaryExpression)
+                if (lambdaExpression.Body is UnaryExpression bodyAsUnaryExpression)
                 {
-                    return bodyAsunaryExpression.Operand;
+                    return bodyAsUnaryExpression.Operand;
                 }
             }
 
@@ -319,6 +324,11 @@ private static List<Expression> CollectExpressions(Expression sourceExpression)
                 list.Add(expression);
             }
 
+            if (expression is MethodCallExpression)
+            {
+                list.Add(expression);
+            }
+
             return list;
         }
     }

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

@@ -352,7 +352,7 @@ Expression ParseIn()
 
                     if (_methodFinder.FindMethod(typeof(IEnumerableSignatures), nameof(IEnumerableSignatures.Contains), false, args, out MethodBase containsSignature) != 1)
                     {
-                        throw ParseError(op.Pos, Res.NoApplicableAggregate, nameof(IEnumerableSignatures.Contains));
+                        throw ParseError(op.Pos, Res.NoApplicableAggregate, nameof(IEnumerableSignatures.Contains), string.Join(",", args.Select(a => a.Type.Name).ToArray()));
                     }
 
                     var typeArgs = new[] { left.Type };
@@ -1738,7 +1738,7 @@ Expression ParseAggregate(Expression instance, Type elementType, string methodNa
 
             if (!_methodFinder.ContainsMethod(typeof(IEnumerableSignatures), methodName, false, args))
             {
-                throw ParseError(errorPos, Res.NoApplicableAggregate, methodName);
+                throw ParseError(errorPos, Res.NoApplicableAggregate, methodName, string.Join(",", args.Select(a => a.Type.Name).ToArray()));
             }
 
             Type callType = typeof(Enumerable);

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

@@ -44,7 +44,7 @@ internal static class Res
         public const string MinusCannotBeAppliedToUnsignedInteger = "'-' cannot be applied to unsigned integers.";
         public const string MissingAsClause = "Expression is missing an 'as' clause";
         public const string NeitherTypeConvertsToOther = "Neither of the types '{0}' and '{1}' converts to the other";
-        public const string NoApplicableAggregate = "No applicable aggregate method '{0}' exists";
+        public const string NoApplicableAggregate = "No applicable aggregate method '{0}({1})' exists";
         public const string NoApplicableIndexer = "No applicable indexer exists in type '{0}'";
         public const string NoApplicableMethod = "No applicable method '{0}' exists in type '{1}'";
         public const string NoItInScope = "No 'it' is in scope";

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

@@ -1,11 +1,11 @@
-using System.Collections.Generic;
+using Newtonsoft.Json.Linq;
+using NFluent;
+using System.Collections.Generic;
 using System.Dynamic;
 using System.Globalization;
 using System.Linq.Dynamic.Core.Exceptions;
 using System.Linq.Dynamic.Core.Tests.Helpers;
 using System.Linq.Dynamic.Core.Tests.Helpers.Models;
-using Newtonsoft.Json.Linq;
-using NFluent;
 using Xunit;
 
 namespace System.Linq.Dynamic.Core.Tests
@@ -1381,13 +1381,40 @@ public void ExpressionTests_NullPropagating(string test, string query)
             Check.That(queryAsString).Equals(query);
         }
 
+        [Fact]
+        public void ExpressionTests_NullPropagation_Method()
+        {
+            // Arrange
+            var users = new[] { new User { Roles = new List<Role>() } }.AsQueryable();
+
+            // Act
+            var resultDynamic = users.Select("np(Roles.FirstOrDefault(false).Name)").ToDynamicArray();
+
+            // Assert
+            Assert.True(resultDynamic[0] == null);
+        }
+
+        [Fact]
+        public void ExpressionTests_NullPropagation_Method_WithDefaultValue()
+        {
+            // Arrange
+            var defaultRoleName = "x";
+            var users = new[] { new User { Roles = new List<Role>() } }.AsQueryable();
+
+            // Act
+            var resultDynamic = users.Select("np(Roles.FirstOrDefault(false).Name, @0)", defaultRoleName).ToDynamicArray();
+
+            // Assert
+            Assert.True(resultDynamic[0] == "x");
+        }
+
         [Fact]
         public void ExpressionTests_NullPropagating_DateTime()
         {
             // Arrange
             var q = new[]
             {
-                new { id = 1, date1 = (DateTime?) DateTime.Now, date2 = DateTime.Now.AddDays(-1)}
+                new { id = 1, date1 = (DateTime?) DateTime.Now, date2 = DateTime.Now.AddDays(-1) }
             }.AsQueryable();
 
             // Act
@@ -1399,7 +1426,7 @@ public void ExpressionTests_NullPropagating_DateTime()
         }
 
         [Fact]
-        public void ExpressionTests_NullPropagating_NullableDateTime()
+        public void ExpressionTests_NullPropagation_NullableDateTime()
         {
             // Arrange
             var q = new[]
@@ -1448,7 +1475,7 @@ public void ExpressionTests_NullPropagating_WithDefaultValue()
         }
 
         [Fact]
-        public void ExpressionTests_NullPropagating_ThrowsException()
+        public void ExpressionTests_NullPropagation_ThrowsException()
         {
             // Arrange
             var q = User.GenerateSampleModels(1, true).AsQueryable();