Please merge - minimal change, huge impact for users of FlexForm hook processors

The argument is already available, passed to the function in each
of the modified classes - the bugfix simply consists of transferring
the argument which is already there and already supported by the
methods called.

Change-Id: If246fdf0dfc071306d23c1273b1f31b1f6b0ae32
Fixes: #39527
Releases: 6.0