code: @Nonnull
    public EChange clearCache ()
    {
      return m_aRWLock.writeLocked ( () -> {
        if (m_aImageData.isEmpty () && m_aNonExistingResources.isEmpty ())
          return EChange.UNCHANGED;
  
        m_aImageData.clear ();
        m_aNonExistingResources.clear ();
  
        if (LOGGER.isDebugEnabled ())
          LOGGER.debug ("Cache was cleared: " + ImageDataManager.class.getName ());
        return EChange.CHANGED;
      });
    }
docs: Remove all cached elements
  
  @return {@link EChange} - never null