docstr: Adds a masked language modeling head on top of the model.
  
  Args:
      head_name (str): The name of the head.
      activation_function (str, optional): Activation function. Defaults to 'gelu'.
      overwrite_ok (bool, optional): Force overwrite if a head with the same name exists. Defaults to False.
docstr_tok: ["Adds","a","masked","language","modeling","head","on","top","of","the","model",".","Args",":","head_name","(","str",")",":","The","name","of","the","head",".","activation_function","(","str",",","optional",")",":","Activation","function",".","Defaults","to","'gelu","'",".","overwrite_ok","(","bool",",","optional",")",":","Force","overwrite","if","a","head","with","the","same","name","exists",".","Defaults","to","False","."]
code: def add_masked_lm_head(
      self, head_name, activation_function="gelu", overwrite_ok=False
  ):
      """
      Adds a masked language modeling head on top of the model.
  
      Args:
          head_name (str): The name of the head.
          activation_function (str, optional): Activation function. Defaults to 'gelu'.
          overwrite_ok (bool, optional): Force overwrite if a head with the same name exists. Defaults to False.
      """
      head = BertStyleMaskedLMHead(
          self, head_name, activation_function=activation_function
      )
      self.add_prediction_head(head, overwrite_ok=overwrite_ok)
  
imports: import torch.nn
  from transformers.models.distilbert.modeling_distilbert import DISTILBERT_INPUTS_DOCSTRING, DISTILBERT_START_DOCSTRING, DistilBertModel, DistilBertPreTrainedModel
  from transformers.utils import add_start_docstrings, add_start_docstrings_to_model_forward
  from ...heads import BertStyleMaskedLMHead, BiaffineParsingHead, CausalLMHead, ClassificationHead, ModelWithFlexibleHeadsAdaptersMixin, MultiLabelClassificationHead, MultipleChoiceHead, QuestionAnsweringHead, TaggingHead
  from ...model_mixin import EmbeddingAdaptersWrapperMixin
  from ...wrappers import init
label_desc: Use image node_id 11 for calling the DistilBertAdapterModel obj's underlying member method code with example usage: obj.add_masked_lm_head(head_name, activation_function, overwrite_ok) without return types