Determine whether it is empty

How to judge whether the parameter is empty, or whether the value of a cell is empty, etc.

There are two cases for null, one is the value is null, then the judgment formula is for example $para==null; the other is the value is an empty string, then the judgment formula is $para=='', if it is not clear enough, the judgment may be unsuccessful due to use incorrectly.

You can ignore whether it is null or an empty string, we recommend using len($para)==0 to determine whether the value is null or an empty string. This way, the problem of whether the value is null or an empty string can be avoided.