def check_for_unassigned_atom(mol):
    """
    Check there isn't a missing atom group ie. '*'
    A '*' in a SMILES string is an atom with an atomic num of 0
    """
    if mol is None:
        return None

    try:
        atoms = mol.GetAtoms()
    except:
        return None

    for atom in atoms:
        if atom.GetAtomicNum()==0:
            return None
    return mol