code: func (actor *Actor) UnsetEnvironmentVariableByApplicationNameAndSpace(appName string, spaceGUID string, environmentVariableName string) (Warnings, error) {
  	app, warnings, appErr := actor.GetApplicationByNameAndSpace(appName, spaceGUID)
  	if appErr != nil {
  		return warnings, appErr
  	}
  	envGroups, getWarnings, getErr := actor.CloudControllerClient.GetApplicationEnvironment(app.GUID)
  	warnings = append(warnings, getWarnings...)
  	if getErr != nil {
  		return warnings, getErr
  	}
  
  	if _, ok := envGroups.EnvironmentVariables[environmentVariableName]; !ok {
  		return warnings, actionerror.EnvironmentVariableNotSetError{EnvironmentVariableName: environmentVariableName}
  	}
  
  	_, patchWarnings, patchErr := actor.CloudControllerClient.UpdateApplicationEnvironmentVariables(
  		app.GUID,
  		ccv3.EnvironmentVariables{
  			environmentVariableName: {Value: "", IsSet: false},
  		})
  	warnings = append(warnings, patchWarnings...)
  	return warnings, patchErr
  }
docs: // UnsetEnvironmentVariableByApplicationNameAndSpace removes an enviornment
  // variable from an application. It must be restarted for changes to take
  // effect.