MemberAdminWindow: Add member data sheet show button

Elwig/Documents/MemberDataSheet.cshtml

@@ -16,7 +16,7 @@
                 <th>Mitglieds-Nr.</th>
                 <td>@Model.Member.MgNr</td>
                 <th>Vorgänger MgNr.</th>
-                <td>@(Model.Member.PredecessorMgNr != null ? Model.Member.PredecessorMgNr : "-")</td>
+                <td>@Model.Member.PredecessorMgNr</td>
             </tr>
             <tr>
                 <th>Titel (vorangestellt)</th>
@@ -36,7 +36,7 @@
             </tr>
             <tr>
                 <th>Geburtsjahr/-tag</th>
-                <td colspan="3">@(Model.Member.Birthday == null ? "-" : string.Join('.', Model.Member.Birthday.Split('-').Reverse()))</td>
+                <td colspan="3">@(string.Join('.', Model.Member.Birthday?.Split('-')?.Reverse()??Array.Empty<string>()))</td>
             </tr>
         </tbody>