code: def testMergeOutputsByKeyEmptyInput(self):
      outputs = []
      outputs_pcoll = [outputs]
      merged_outputs_pcolls = tuple(
          outputs_pcoll
          | beam.FlatMap(
              analyzer_impls._merge_outputs_by_key,
              outputs_dtype=[tf.float32, tf.float32],
          ).with_outputs("key", "0", "1")
      )
      self.assertAllEqual(merged_outputs_pcolls[0][0], np.array([]))
      self.assertAllEqual(merged_outputs_pcolls[1][0], np.array([]))
      self.assertAllEqual(merged_outputs_pcolls[2][0], np.array([]))
  
file_path: transform/tensorflow_transform/beam/analyzer_impls_test.py
imports: import apache_beam
  import numpy
  import tensorflow
  from tensorflow_transform.beam import analyzer_impls
  from tensorflow_transform.beam import tft_unit
label_desc: Use image node_id 3 for calling the AnalyzerImplsTest obj's underlying member method code with example usage: obj.testMergeOutputsByKeyEmptyInput() without return types