code: @Override
      protected Map<String, List<Object>> mergePersonAttributes(final Map<String, List<Object>> toModify, final Map<String, List<Object>> toConsider) {
          Validate.notNull(toModify, "toModify cannot be null");
          Validate.notNull(toConsider, "toConsider cannot be null");
  
          for (final Map.Entry<String, List<Object>> sourceEntry : toConsider.entrySet()) {
              final String sourceKey = sourceEntry.getKey();
  
              List<Object> destList = toModify.get(sourceKey);
              if (destList == null) {
                  destList = new LinkedList<>();
                  toModify.put(sourceKey, destList);
              }
  
              final List<Object> sourceValue = sourceEntry.getValue();
              destList.addAll(sourceValue);
          }
  
          return toModify;
      }
docs: /* (non-Javadoc)
  @see org.jasig.services.persondir.support.merger.BaseAdditiveAttributeMerger#mergePersonAttributes(java.util.Map, java.util.Map)