code: def merge_molecular_fragments(
      molecules: List[MolecularFragment],
  ) -> Optional[MolecularFragment]:
      """Helper method to merge two molecular fragments.
  
      Parameters
      ----------
      molecules: List[MolecularFragment]
          List of `MolecularFragment` objects.
  
      Returns
      -------
      Optional[MolecularFragment]
          Returns a merged `MolecularFragment`
      """
      if len(molecules) == 0:
          return None
      if len(molecules) == 1:
          return molecules[0]
      else:
          all_atoms = []
          all_coords = []
          for mol_frag in molecules:
              all_atoms += mol_frag.GetAtoms()
              all_coords.append(mol_frag.GetCoords())
          return MolecularFragment(
              all_atoms, np.concatenate(all_coords)
          )
  
imports: import itertools
  import numpy
  from typing import List, Optional, Sequence, Set, Tuple, Union
  import logging
  from deepchem.utils.typing import RDKitAtom, RDKitMol
  from deepchem.utils.geometry_utils import compute_pairwise_distances
label_desc: Use image node_id 2 for calling a global function with example usage: merge_molecular_fragments(molecules) and returns: None, molecules, MolecularFragment