code: private void internalSetParent(CommandRegistry parentRegistry) {
          
          if (!ObjectUtils.nullSafeEquals(this.parent, parentRegistry)) {
              
              if (this.parent != null) {
                  this.parent.removeCommandRegistryListener(this);
              }
              
              this.parent = parentRegistry;
              
              if (this.parent != null) {
                  this.parent.addCommandRegistryListener(this);
              }
              
          }
          
      }
docs: This method is provided as a private helper so that it can be called by the constructor,
  instead of the constructor having to call the public overridable setParent method.