wro4j-core/src/main/java/ro/isdc/wro/model/resource/processor/factory/ConfigurableProcessorsFactory.java
private Map<String, ResourcePreProcessor> getPreProcessorsMap() {
    if (this.preProcessorsMap == null) {
      synchronized (this) {
        if (this.preProcessorsMap == null) {
          this.preProcessorsMap = newPreProcessorsMap();
        }
      }
    }
    return this.preProcessorsMap;
  }
private Map<String, ResourcePreProcessor> getPreProcessorsMap() {
    if (this.preProcessorsMap == null) {
      synchronized (this) {
        if (this.preProcessorsMap == null) {
          this.preProcessorsMap = newPreProcessorsMap();
        }
      }
    }
    return this.preProcessorsMap;
  }
To be used for internal usage. Ensure that returned object is not null.