Show ‘-‘ when group is null

Author: Baspa

src/Filament/RelationManagers/FieldsRelationManager.php

@@ -167,6 +167,7 @@ public function table(Table $table): Table
             ->groups([
                 Group::make('group')
                     ->label(__('Group'))
+                    ->getTitleFromRecordUsing(fn ($record): string => filled($record->group) ? $record->group : '-')
             ])
             ->columns([
                 Tables\Columns\TextColumn::make('name')