AttributeError: 'NoneType' object has no attribute 'GetDistance'

[rezkirasyak]

Traceback (most recent call last):
File "/home/rezkirasyak/miniconda3/envs/hippos/bin/hippos", line 10, in
sys.exit(main())
File "/home/rezkirasyak/miniconda3/envs/hippos/lib/python3.6/site-packages/pyplif_hippos/hippos.py", line 49, in main
bitstrings = get_bitstring(docking_results, hippos_config)
File "/home/rezkirasyak/miniconda3/envs/hippos/lib/python3.6/site-packages/pyplif_hippos/ifp_processing.py", line 63, in get_bitstring
residue_obj[name].calculateIFPPlants(ligands, flex_protein, ligand_atom_group)
File "/home/rezkirasyak/miniconda3/envs/hippos/lib/python3.6/site-packages/pyplif_hippos/ifp_processing.py", line 809, in calculateIFPPlants
distance = ligand_atom.GetDistance(atom)
AttributeError: 'NoneType' object has no attribute 'GetDistance'