code: def test_pipeline_builder_merge_many_to_many_undefined():
      builder_one_to_many = (
          PipelineBuilder()
          .add_node("operation_c")
          .add_branch("operation_g", "operation_a")
      )
      builder_many_to_many = (
          PipelineBuilder()
          .add_branch("operation_b", "operation_d")
          .grow_branches("operation_f", "operation_h")
      )
      # many to many result undefined
      assert (
          merge_pipeline_builders(
              builder_one_to_many, builder_many_to_many
          )
          is None
      )
  
imports: from copy import copy
  from fedot.core.pipelines.pipeline_builder import PipelineBuilder, merge_pipeline_builders
  from fedot.core.pipelines.node import PipelineNode
  from fedot.core.pipelines.pipeline import Pipeline
  from test.unit.dag.test_graph_utils import graphs_same
label_desc: Use image node_id 14 for calling a global function with example usage: test_pipeline_builder_merge_many_to_many_undefined() without return types