correct test on creation of Bound/Partner complexes

ippisite/ippidb/management/commands/import_v1_data.py

@@ -171,7 +171,7 @@ select distinct protein.NumUniprot, domain.PfamNumAccession  , complexe.NbCopy,
                     else:
                         ppi = Ppi.objects.get(id=ppi_ids_mapping[row[6]])
                     # create a complex
-                    if row[3]=="null":
+                    if row[3] is None:
                         c = ProteinDomainPartnerComplex()
                     else:
                         c = ProteinDomainBoundComplex()