fix: improve handling for other fields

* fix show_dates
* fix _identifiers_for_group
* fix show_related_identifiers by filtering with selectattr: https://jinja.palletsprojects.com/en/stable/templates/#jinja-filters.selectattr

invenio_app_rdm/records_ui/templates/semantic-ui/invenio_app_rdm/records/macros/detail.html

@@ -82,7 +82,7 @@ <h2>{{ add_description.type.title_l10n if add_description.type is defined else _
 
 {% macro show_dates(dates) %}
   {% for date in dates %}
-    <dt class="ui tiny header">{{ date.type.title_l10n }}</dt>
+  <dt class="ui tiny header">{{ date.type.title_l10n if date.type is defined else 'Unknown date type' }}</dt>
     <dd>
       <div>{{ date.date }}</div>
       <div class="text-muted">{{ date.description }}</div>
@@ -160,24 +160,27 @@ <h2>{{ add_description.type.title_l10n if add_description.type is defined else _
         {{ identifier.resource_type.title_l10n }}:
       {% endif %}
 
-      {% set url = identifier.identifier|pid_url %}
+      {% set ident_val = identifier.identifier if identifier.identifier is defined else '' %}
+      {% set url = ident_val|pid_url %}
       {% if url %}
         <a href="{{ url }}" target="_blank" title="{{ _('Opens in new tab') }}">
-          {{ identifier.identifier }}
+          {{ ident_val }}
         </a>
       {% else %}
-        {{ identifier.identifier }}
+        {{ ident_val }}
       {% endif %}
 
-      {{ ' (' + identifier.scheme | get_scheme_label + ')' }}
+      {% if identifier.scheme is defined %}
+        {{ ' (' ~ (identifier.scheme|get_scheme_label) ~ ')' }}
+      {% endif %}
     </dd>
   {% endfor %}
 {% endmacro %}
 
 
 {% macro show_related_identifiers(related_identifiers) %}
   <dl class="details-list">
-    {%- for group in related_identifiers | groupby('relation_type.title_l10n') %}
+    {%- for group in (related_identifiers|selectattr("relation_type","defined")|list) | groupby('relation_type.title_l10n') %}
       <dt class="ui tiny header">{{ group.grouper }}</dt>
       {{ _identifiers_for_group(group.list) }}
     {%- endfor %}