Better handling of errors on trial license request (#14886)

* Fix behavior on blank site url on trial requests

* Adding trial license error response handling

* Changing text based on PR review comments

api4/license.go

@@ -187,6 +187,11 @@ func requestTrialLicense(c *Context, w http.ResponseWriter, r *http.Request) {
 		Users:    usersNumber.Users,
 	}
 
+	if trialLicenseRequest.SiteURL == "" {
+		c.Err = model.NewAppError("RequestTrialLicense", "api.license.request_trial_license.no-site-url.app_error", nil, "", http.StatusBadRequest)
+		return
+	}
+
 	if err := c.App.Srv().RequestTrialLicense(trialLicenseRequest); err != nil {
 		c.Err = err
 		return

app/license.go

@@ -218,6 +218,10 @@ func (s *Server) RequestTrialLicense(trialRequest *model.TrialLicenseRequest) *m
 	defer resp.Body.Close()
 	licenseResponse := model.MapFromJson(resp.Body)
 
+	if _, ok := licenseResponse["license"]; !ok {
+		return model.NewAppError("RequestTrialLicense", "api.license.request_trial_license.app_error", nil, licenseResponse["message"], http.StatusBadRequest)
+	}
+
 	if _, err := s.SaveLicense([]byte(licenseResponse["license"])); err != nil {
 		return err
 	}

i18n/en.json

@@ -1504,6 +1504,10 @@
     "id": "api.license.request_trial_license.app_error",
     "translation": "Unable to get a trial license, please try again or contact with support@mattermost.com."
   },
+  {
+    "id": "api.license.request_trial_license.no-site-url.app_error",
+    "translation": "Unable to request a trial license. Please configure a Site URL in the web server section of the Mattermost System Console."
+  },
   {
     "id": "api.marshal_error",
     "translation": "marshal error"