refactor: move null check at the top of convertToDatabaseValue() method

Author: landure

src/MartinGeorgiev/Doctrine/DBAL/Types/Ltree.php

@@ -65,6 +65,10 @@ public function convertToDatabaseValue($value, AbstractPlatform $platform): ?str
     {
         $this->assertPostgreSQLPlatform($platform);
 
+        if (null === $value) {
+            return null;
+        }
+
         if (\is_string($value)) {
             try {
                 $value = LtreeValueObject::fromString($value);
@@ -77,10 +81,6 @@ public function convertToDatabaseValue($value, AbstractPlatform $platform): ?str
             return (string) $value;
         }
 
-        if (null === $value) {
-            return null;
-        }
-
         throw InvalidLtreeForPHPException::forInvalidType($value);
     }