code: def add_reference_analysis(self, reference, service, slot, ref_gid=None):
          
          if not reference or not service:
              return None
  
          if not IReferenceSample.providedBy(reference):
              logger.warning('Cannot create reference analysis from a non '
                             'reference sample: {}'.format(reference.getId()))
              return None
  
          calc = service.getCalculation()
          if calc and calc.getDependentServices():
              logger.warning('Cannot create reference analyses with dependent'
                             'services: {}'.format(service.getId()))
              return None
  
          # Create the reference analysis
          ref_analysis = reference.addReferenceAnalysis(service)
          if not ref_analysis:
              logger.warning("Unable to create a reference analysis for "
                             "reference '{0}' and service '{1}'"
                             .format(reference.getId(), service.getKeyword()))
              return None
  
          # Set ReferenceAnalysesGroupID (same id for the analyses from
          # the same Reference Sample and same Worksheet)
          gid = ref_gid and ref_gid or self.nextRefAnalysesGroupID(reference)
          ref_analysis.setReferenceAnalysesGroupID(gid)
  
          # Add the reference analysis into the worksheet
          self.setAnalyses(self.getAnalyses() + [ref_analysis, ])
          self.addToLayout(ref_analysis, slot)
  
          # Reindex
          ref_analysis.reindexObject(idxs=["getAnalyst", "getWorksheetUID",
                                           "getReferenceAnalysesGroupID"])
          self.reindexObject(idxs=["getAnalysesUIDs"])
          return ref_analysis
docs: Creates a reference analysis in the destination slot (dest_slot) passed
          in, by using the reference and service_uid. If the analysis
          passed in is not an IReferenceSample or has dependent services, returns
          None. If no reference analyses group id (refgid) is set, the value will
          be generated automatically.
          :param reference: reference sample to create an analysis from
          :param service: the service object to create an analysis from
          :param slot: slot where the reference analysis must be stored
          :param refgid: the reference analyses group id to be set
          :return: the reference analysis or None