For some molecules, pubchem doesn't distinguish between between isomeric and canonical SMILES and has only SMILES, making the retrieval fail. The functions to query canonical and isomeric smiles should be updated to supply the "standard" SMILES code if there is no distinction, therefore the queried ISOMERIC_SMILES or CANONICAL_SMILES should be filled with the value stored under SMILES if neither ISOMERIC_SMILES nor CANONICAL_SMILES are present.
For some molecules, pubchem doesn't distinguish between between isomeric and canonical SMILES and has only SMILES, making the retrieval fail. The functions to query canonical and isomeric smiles should be updated to supply the "standard" SMILES code if there is no distinction, therefore the queried ISOMERIC_SMILES or CANONICAL_SMILES should be filled with the value stored under SMILES if neither ISOMERIC_SMILES nor CANONICAL_SMILES are present.