Implement containsKey for HttpHeaders returned from ServletServerHttpResponse [SPR-13668] #18243
As currently implemented
I'm logging this issue pretty quickly so I don't forget. There may be other methods on
Note that this impacts the fix for #18124 since the intent is to only set the Content-Disposition if it has not been set.
Affects: 4.1.8, 4.2.2
Backported to: 4.1.9