code: def merge_molecules(molecules):
      """Helper method to merge two molecules.
  
      Parameters
      ----------
      molecules: list
          List of rdkit molecules
  
      Returns
      -------
      merged: rdkit molecule
      """
      from rdkit.Chem import rdmolops
  
      if len(molecules) == 0:
          return None
      elif len(molecules) == 1:
          return molecules[0]
      else:
          combined = molecules[0]
          for nextmol in molecules[1:]:
              combined = rdmolops.CombineMols(combined, nextmol)
          return combined
  
imports: import os
  import logging
  import itertools
  import numpy
  from io import StringIO
  from deepchem.utils.pdbqt_utils import pdbqt_to_pdb
  from deepchem.utils.pdbqt_utils import convert_mol_to_pdbqt
  from deepchem.utils.pdbqt_utils import convert_protein_to_pdbqt
  from deepchem.utils.geometry_utils import compute_pairwise_distances
  from deepchem.utils.geometry_utils import compute_centroid
  from deepchem.utils.fragment_utils import MolecularFragment
  from deepchem.utils.fragment_utils import MoleculeLoadException
  from typing import Any, List, Sequence, Tuple, Set, Optional, Dict, Union
  from deepchem.utils.typing import OneOrMany, RDKitMol
label_desc: Use image node_id 9 for calling a global function with example usage: merge_molecules(molecules) and returns: None, molecules, combined