fix: OCI8 getFieldData() returns incorrect default value

Author: kenjis

system/Database/OCI8/Connection.php

@@ -315,11 +315,7 @@ protected function _fieldData(string $table): array
 
             $retval[$i]->max_length = $length;
 
-            $default = $query[$i]->DATA_DEFAULT;
-            if ($default === null && $query[$i]->NULLABLE === 'N') {
-                $default = '';
-            }
-            $retval[$i]->default  = $default;
+            $retval[$i]->default  = $query[$i]->DATA_DEFAULT;
             $retval[$i]->nullable = $query[$i]->NULLABLE === 'Y';
         }