code: public I_CmsPrincipal lookupPrincipal(CmsDbContext dbc, String principalName) {
  
          try {
              CmsGroup group = getUserDriver(dbc).readGroup(dbc, principalName);
              if (group != null) {
                  return group;
              }
          } catch (Exception e) {
              // ignore this exception
          }
  
          try {
              CmsUser user = readUser(dbc, principalName);
              if (user != null) {
                  return user;
              }
          } catch (Exception e) {
              // ignore this exception
          }
  
          return null;
      }
docs: Lookup and read the user or group with the given name.<p>
  
  @param dbc the current database context
  @param principalName the name of the principal to lookup
  
  @return the principal (group or user) if found, otherwise <code>null</code>