BUG Fix PostgreSQL issue in TreeMultiselectField where field would try to filter list by a blank ID

src/Forms/TreeMultiselectField.php

@@ -149,12 +149,16 @@ class TreeMultiselectField extends TreeDropdownField
 
         // Parse ids from value string / array
         $ids = [];
+
         if (is_string($value)) {
             $ids = preg_split("#\s*,\s*#", trim($value));
         } elseif (is_array($value)) {
             $ids = array_values($value);
         }
 
+        // Filter out empty strings
+        $ids = array_filter($ids);
+
         // No value
         if (empty($ids)) {
             return ArrayList::create();

tests/php/Forms/TreeMultiselectFieldTest.php

@@ -340,5 +340,12 @@ class TreeMultiselectFieldTest extends SapphireTest
             [],
             $field->getItems()
         );
+
+        // Andle empty string none value
+        $field->setValue('');
+        $this->assertListEquals(
+            [],
+            $field->getItems()
+        );
     }
 }