Emlog6.0标签不存在提示SQL执行错误的解决办法

SQL语句执行错误: SELECT `gid` FROM `emlog_tag` WHERE `tid` =
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1

function getTagByName($tagName) {
        $tagId = $this->getIdFromName($tagName);
	return $this->getTagById($tagId); 
    }

function getTagByName($tagName) {
        $tagId = $this->getIdFromName($tagName);
		if ($tagId) {
			return $this->getTagById($tagId); 
		}else{
			return false;
		}	
    }