Prevent writing of empty string to json if mature lookup fails.

scripts/convert_signalp.py

@@ -45,12 +45,10 @@ with open(filename) as f:
                     })
 
                 if include_mature:
-                    mature_seq = ''
                     try:
-                        mature_seq = mature[split[0]]
+                        results[-1]['mature sequence'] = mature[split[0]]
                     except ValueError:
-                        print('SignalP Converter: No mature sequence received for protein: {}, although signal peptide present!'.format(split[0]))
-                    results[-1]['mature sequence'] = mature_seq
+                        print('SignalP Converter: No mature sequence received for protein {}, although signal peptide present!'.format(split[0]))
             else:
                 results.append({'signalpeptide': False})
         else: