関連ワード:  java check if variable is null    java check if variable is null or empty    java check if var is null    how to check if variable is null in python    how to check if variable is null in javascript    how to check if variable is null    how to check if variable is null or undefined in javascript    how to check if variable is null in php    how to check if variable is null in shell script    how to check if variable is null in powershell