code: public LabelId convertToId(Label label) {
          if (transactionCache.isLabelCached(label)) {
              return transactionCache.convertLabelToId(label);
          }
          return LabelId.invalid();
      }
docs: Converts a Type Label into a type Id for this specific graph. Mapping labels to ids will differ between graphs
  so be sure to use the correct graph when performing the mapping.
  
  @param label The label to be converted to the id
  @return The matching type id