Checking MR status date for related MR status tooltip

Changed related MR status tooltip content when MR status date
is not available.

app/views/projects/issues/_merge_requests_status.html.haml

@@ -12,11 +12,14 @@
   - mr_status_class = 'closed'
 - else
   - mr_status_date = merge_request.created_at
-  - mr_status_title = _('Opened')
+  - mr_status_title = mr_status_date ? _('Opened') : _('Open')
   - mr_status_icon = 'issue-open-m'
   - mr_status_class = 'open'
-- mr_status_tooltip = "<div><span class=\"bold\">#{mr_status_title}</span> #{time_ago_in_words(mr_status_date)} ago</div><span class=\"text-tertiary\">#{l(mr_status_date.to_time, format: time_format)}</span>"
+- if mr_status_date
+  - mr_status_tooltip = "<div><span class=\"bold\">#{mr_status_title}</span> #{time_ago_in_words(mr_status_date)} ago</div><span class=\"text-tertiary\">#{l(mr_status_date.to_time, format: time_format)}</span>"
+- else
+  - mr_status_tooltip = "<div><span class=\"bold\">#{mr_status_title}</span></div>"
 %span.mr-status-wrapper.suggestion-help-hover{ class: css_class, data: { toggle: 'tooltip', placement: 'bottom', html: 'true', title: mr_status_tooltip } }
   = sprite_icon(mr_status_icon, size: 16, css_class: "merge-request-status #{mr_status_class}")