関連ワード:  powershell check if variable is null    powershell check if variable is null or empty    powershell check if var is null    powershell check if variable is empty    powershell check if variable is empty string    powershell check if variable is not null    powershell check if var is empty    powershell test if variable is empty    powershell check if variable is null or empty string    powershell check if var is null or empty