code: public String getGlobusID(String userID) {
          if (userID == null) {
              throw new IllegalArgumentException(i18n.getMessage("userIdNull"));
          }
  
          if (this.map == null) {
              return null;
          }
  
          Iterator iter = this.map.entrySet().iterator();
          Map.Entry mapEntry;
          GridMapEntry entry;
          while(iter.hasNext()) {
              mapEntry = (Map.Entry)iter.next();
              entry = (GridMapEntry)mapEntry.getValue();
              if (entry.containsUserID(userID)) {
                  return entry.getGlobusID();
              }
          }
          return null;
      }
docs: Returns globus ID associated with the
  specified local user name.
  
  @param userID local user name
  @return associated globus ID, null
  if there is not any.