code: def validate_non_nullable_fields(
      cls, values: Dict[str, Any]
  ) -> Dict[str, Any]:
      if cls.__non_nullable_fields__ is None:
          return values
  
      invalid_keys = []
      for key in cls.__non_nullable_fields__:
          if key in values and values[key] is None:
              invalid_keys.append(key)
  
      if invalid_keys:
          raise ValueError(
              f"The following keys must have non-null values: {', '.join(invalid_keys)}"
          )
  
      return values
  
imports: from typing import Any, Dict, Set, Union
  from argilla.server.pydantic_v1 import BaseModel, root_validator
label_desc: Use image node_id 1 for calling the UpdateSchema obj's underlying member method code with example usage: obj.validate_non_nullable_fields(cls, values) and returns: values, values