Strict equality of generic type parameter count

Conflicts:
	src/Nest/Resolvers/Writers/TypeMappingWriter.cs

Author: radiosterne

src/Nest/Resolvers/Writers/TypeMappingWriter.cs

@@ -284,7 +284,7 @@ private static Type GetUnderlyingType(Type type)
 			if (type.IsArray)
 				return type.GetElementType();
 
-			if (type.IsGenericType && type.GetGenericArguments().Length >= 1)
+            if (type.IsGenericType && type.GetGenericArguments().Length == 1 && (type.GetInterface("IEnumerable") != null || Nullable.GetUnderlyingType(type) != null))
 				return type.GetGenericArguments()[0];
 
 			return type;