getFieldMeta<T>  method 
Get metadata from a field
Implementation
// ignore: avoid_shadowing_type_parameters
T getFieldMeta<T>(String name, T defaultValue) {
  if (field.cast.metaData == null || field.cast.metaData![name] == null) {
    return defaultValue;
  }
  return field.cast.metaData![name];
}