ExpressionMapper.VisitAllParametersExpression: Only use generic type argument if destSubTypes extends IEnumerable<>

Author: Michael Croes

src/AutoMapper.Extensions.ExpressionMapping/ExpressionMapper.cs

@@ -173,7 +173,7 @@ private Expression VisitAllParametersExpression<T>(Expression<T> expression)
                     from t in expression.Parameters
                     let sourceParamType = t.Type
                     from destParamType in _destSubTypes.Where(dt => dt != sourceParamType)
-                    let a = destParamType.IsGenericType() ? destParamType.GetTypeInfo().GenericTypeArguments[0] : destParamType
+                    let a = destParamType.IsEnumerableType(out var itemType) ? itemType : destParamType
                     let typeMap = _configurationProvider.ResolveTypeMap(a, sourceParamType)
                     where typeMap != null
                     let oldParam = t

src/AutoMapper.Extensions.ExpressionMapping/TypeExtensions.cs

@@ -171,5 +171,14 @@ public static bool IsQueryableType(this Type type)
 
         public static Type GetGenericElementType(this Type type)
             => type.HasElementType ? type.GetElementType() : type.GetTypeInfo().GenericTypeArguments[0];
+
+        public static bool IsEnumerableType(this Type type, out Type itemType)
+        {
+            itemType = type.GetInterfaces()
+                .FirstOrDefault(t => t.GetGenericTypeDefinitionIfGeneric() == typeof(IEnumerable<>))
+                ?.GetGenericArguments()[0];
+
+            return itemType != null;
+        }
     }
 }