<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _build(self, inputs):
 """Connects the MergeDims module into the graph. Args: inputs: Tensor or a nested list of Tensors to merge. Its rank must be greater than or equal to `start` + `size`. Returns: The merged Tensor or a nested list of merged Tensors. Raises: ValueError: If any of the `inputs` tensors has insufficient rank. """

    if nest.is_sequence(inputs):
      merged_tensors = [self._merge(tensor) for tensor in nest.flatten(inputs)]
      return nest.pack_sequence_as(inputs, merged_tensors)

    # inputs is a single tf.Tensor
    return self._merge(inputs)