fix(doctrine): joinColumn might be an array (api-platform#7060)

fixes api-platform#7052

Author: soyuka

src/Doctrine/Orm/Extension/EagerLoadingExtension.php

@@ -181,7 +181,13 @@ private function joinRelations(QueryBuilder $queryBuilder, QueryNameGeneratorInt
                 $associationAlias = $existingJoin->getAlias();
                 $isLeftJoin = Join::LEFT_JOIN === $existingJoin->getJoinType();
             } else {
-                $isNullable = $mapping['joinColumns'][0]?->nullable ?? true;
+                $joinColumn = $mapping['joinColumns'][0] ?? ['nullable' => true];
+                if (\is_array($joinColumn)) {
+                    $isNullable = $joinColumn['nullable'] ?? true;
+                } else {
+                    $isNullable = $joinColumn->nullable ?? true;
+                }
+
                 $isLeftJoin = false !== $wasLeftJoin || true === $isNullable;
                 $method = $isLeftJoin ? 'leftJoin' : 'innerJoin';