fix: prevent using "<nil>" as default value

Signed-off-by: Russell Centanni <russell.centanni@gmail.com> Signed-off-by: Russell Centanni <russell.centanni@gmail.com>

Author: lizardruss

pkg/devspace/config/loader/variable/undefined_variable.go

@@ -99,7 +99,7 @@ func getParams(variable *latest.Variable) *survey.QuestionOptions {
 params.IsPassword = true
 }
 
-if variable.Default != "" {
+if variable.Default != nil && variable.Default != "" {
 params.DefaultValue = fmt.Sprintf("%v", variable.Default)
 }
 if variable.Default != nil {