[PATCH] c-user: Document rtems_extension_create()

[Sebastian Huber]

Close #3953.
---
 c-user/user_extensions.rst | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/c-user/user_extensions.rst b/c-user/user_extensions.rst
index c3bd1c6..89b86fd 100644
--- a/c-user/user_extensions.rst
+++ b/c-user/user_extensions.rst
@@ -466,6 +466,8 @@ DIRECTIVE STATUS CODES:
 
      * - ``RTEMS_SUCCESSFUL``
        - extension set created successfully
+     * - ``RTEMS_INVALID_ADDRESS``
+       - ``table`` or ``id`` are NULL
      * - ``RTEMS_INVALID_NAME``
        - invalid extension set name
      * - ``RTEMS_TOO_MANY``
-- 
2.16.4