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