code: protected function getProvider($nameOrRelativeOrSubject)
      {
          if (null === $provider = $this->registry->getProvider($nameOrRelativeOrSubject)) {
              throw new SubjectException('Failed to get provider.');
          }
  
          return $provider;
      }
docs: Returns the provider by name or supporting the given relative or subject.
  
  @param string|SubjectRelativeInterface|object $nameOrRelativeOrSubject
  
  @return \Ekyna\Component\Commerce\Subject\Provider\SubjectProviderInterface
  @throws SubjectException