code: protected PrincipalResolver getPrincipalResolverLinkedToHandlerIfAny(final AuthenticationHandler handler, final AuthenticationTransaction transaction) {
          return this.authenticationEventExecutionPlan.getPrincipalResolverForAuthenticationTransaction(handler, transaction);
      }
docs: Gets principal resolver linked to the handler if any.
  
  @param handler     the handler
  @param transaction the transaction
  @return the principal resolver linked to handler if any, or null.