Reset Jenkins password if username was left blank

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/22430

app/models/project_services/jenkins_service.rb

@@ -24,7 +24,7 @@ class JenkinsService < CiService
   before_update :reset_password
   validates :username,
             presence: true,
-            if: ->(service) { service.activated? && service.password.present? }
+            if: ->(service) { service.activated? && service.password_touched? }
 
   default_value_for :push_events, true
   default_value_for :merge_requests_events, false
@@ -34,7 +34,7 @@ class JenkinsService < CiService
 
   def reset_password
     # don't reset the password if a new one is provided
-    if jenkins_url_changed? && !password_touched?
+    if (jenkins_url_changed? || username.blank?) && !password_touched?
       self.password = nil
     end
   end

app/views/shared/_field.html.haml

@@ -13,15 +13,16 @@
   - else
     = form.label name, title, class: "control-label"
   .col-sm-10
-    - if type == 'text'
+    - case type
+    - when 'text'
       = form.text_field name, class: "form-control", placeholder: placeholder
-    - elsif type == 'textarea'
+    - when 'textarea'
       = form.text_area name, rows: 5, class: "form-control", placeholder: placeholder
-    - elsif type == 'checkbox'
+    - when 'checkbox'
       = form.check_box name
-    - elsif type == 'select'
+    - when 'select'
       = form.select name, options_for_select(choices, value ? value : default_choice), {}, { class: "form-control" }
-    - elsif type == 'password'
+    - when 'password'
       = form.password_field name, autocomplete: "new-password", class: 'form-control'
     - if help
       %span.help-block= help