fix callback bug

Author: marksalmon

src/Http/Livewire/LivewireDatatable.php

@@ -278,7 +278,7 @@ public function resolveAdditionalSelects($column)
         return $selects->count() > 1
             ? new Expression("CONCAT_WS('" . static::SEPARATOR . "' ," .
                 collect($selects)->map(function ($select) {
-                    return "IF($select, $select, '')";
+                    return "COALESCE($select, '')";
                 })->join(', ') . ')')
             : $selects->first();
     }

tests/ColumnTest.php

@@ -168,8 +168,9 @@ public function it_returns_width_property_from_column()
             'filterView' => null,
             'select' => null,
             'joins' => null,
+
             'aggregate' => 'group_concat',
-            'align' => 'left',
+            'align' => 'left',gch
             'preventExport' => null,
             'width' => '1em',
             'unsortable' => null,