@RequiresBackgroundThread
  private HashMap<PropertiesFile, IProperty> findExistingProperties(Collection<PropertiesFile> files) {
    final HashMap<PropertiesFile, IProperty> existingProperties = new HashMap<>();
    for (PropertiesFile propertiesFile : files) {
      IProperty existingProperty = propertiesFile.findPropertyByKey(getKey());
      existingProperties.put(propertiesFile, existingProperty);
    }
    return existingProperties;
  }
@RequiresBackgroundThread
  private HashMap<PropertiesFile, IProperty> findExistingProperties(Collection<PropertiesFile> files)