检查当前参数是否为空或者null

 /**
  * 检查当前参数是否为空或者null
  * 如果是空 返回true，否之返回 false
  * return boolean 
  */
 function checkIsEmptyOrNull(param){
    var nullParamFlag = false;
    if("" == param){
        nullParamFlag = true;
    }else if(null == param){
        nullParamFlag = true;
    }else if(undefined == param){
        nullParamFlag = true;
    }else if("undefined" == param){
        nullParamFlag = true;
    }else if("null" == param){
        nullParamFlag = true;
    }
    return nullParamFlag;
 }