Fixed : calling methods which returns a nullable (#382)

Author: StefH

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

@@ -88,12 +88,14 @@ public static bool IsPredefinedType(ParsingConfig config, Type type)
             Check.NotNull(config, nameof(config));
             Check.NotNull(type, nameof(type));
 
-            if (PredefinedTypes.ContainsKey(type))
+            var nonNullableType = TypeHelper.GetNonNullableType(type);
+            if (PredefinedTypes.ContainsKey(nonNullableType))
             {
                 return true;
             }
 
-            return config.CustomTypeProvider != null && config.CustomTypeProvider.GetCustomTypes().Contains(type);
+            return config.CustomTypeProvider != null && 
+                   (config.CustomTypeProvider.GetCustomTypes().Contains(type) || config.CustomTypeProvider.GetCustomTypes().Contains(nonNullableType));
         }
     }
 }

test/System.Linq.Dynamic.Core.Tests/QueryableTests.Methods.cs

@@ -0,0 +1,64 @@
+using Xunit;
+
+namespace System.Linq.Dynamic.Core.Tests
+{
+    public partial class QueryableTests
+    {
+        [Fact]
+        public void CallMethod()
+        {
+            // Arrange
+            var query = new[] { new Test() }.AsQueryable();
+
+            // Act
+            var result = query.Select<decimal>("t => t.GetDecimal()").First();
+
+            // Assert
+            Assert.Equal(42, result);
+        }
+
+        [Fact]
+        public void CallMethodWhichReturnsNullable()
+        {
+            // Arrange
+            var query = new[] { new Test() }.AsQueryable();
+
+            // Act
+            var result = query.Select<decimal?>("t => t.GetNullableDecimal()").First();
+
+            // Assert
+            Assert.Equal(null, result);
+        }
+
+        [Fact]
+        public void CallMethodWhichReturnsNullable_WithValue()
+        {
+            // Arrange
+            var query = new[] { new Test() }.AsQueryable();
+
+            // Act
+            var result = query.Select<decimal?>("t => t.GetNullableDecimalWithValue()").First();
+
+            // Assert
+            Assert.Equal(100, result);
+        }
+    }
+
+    class Test
+    {
+        public decimal GetDecimal()
+        {
+            return 42;
+        }
+
+        public decimal? GetNullableDecimal()
+        {
+            return null;
+        }
+
+        public decimal? GetNullableDecimalWithValue()
+        {
+            return 100;
+        }
+    }
+}