SyncGenerator::associateToLearndash( $ldGroupId = null )

	public function associateToLearndash($ldGroupId = null)
	{
		if ($this->ldGroupId && ! $ldGroupId) {
			return $this;
		}

		$this->syncingToLearndash(function() use ($ldGroupId) {
			$ldGroup = get_post($ldGroupId);

			if (! $ldGroupId || ! $ldGroup) {
				$this->createLearndashGroup();
			} else {
				$this->unsetBpGroupMeta(false)->unsetLdGroupMeta(false);
				$this->ldGroupId = $ldGroupId;
			}

    		$this->setSyncGropuIds();
		});

		return $this;
	}