public static void WriteNonNullType(
     this DocumentWriter writer,
     NonNullTypeNode node)
 {
     writer.WriteType(node.Type);
     writer.Write('!');
 }
 public static void WriteListType(
     this DocumentWriter writer,
     ListTypeNode node)
 {
     writer.Write('[');
     writer.WriteType(node.Type);
     writer.Write(']');
 }