class_docstr: An operator that combines output blocks from
  two or more input operators into a single output.
code: def all_inputs_done(self) -> None:
      # Note that in the case where order is not preserved, all inputs
      # are directly added to the output buffer as soon as they are received,
      # so there is no need to check any intermediary buffers.
      if self._preserve_order:
          for idx, input_buffer in enumerate(self._input_buffers):
              assert len(input_buffer) == 0, (
                  f"Input at index {idx} still has "
                  f"{len(input_buffer)} blocks remaining."
              )
      super().all_inputs_done()
  
file_path: ray/python/ray/data/_internal/execution/operators/union_operator.py
imports: from typing import List
  from ray.data._internal.execution.interfaces import ExecutionOptions, PhysicalOperator, RefBundle
  from ray.data._internal.execution.operators.base_physical_operator import NAryOperator
  from ray.data._internal.stats import StatsDict
label_desc: Use image node_id 6 for calling the UnionOperator obj's underlying member method code with example usage: obj.all_inputs_done() without return types