Fixes issue #2228 (previous pull request that fixed this was closed due to me stuffing up ;-) )
Replaced foreach with array_walk
If the value = null don't output December 31, 1999

Just output null (the value)
Fixed #2230: meta keywords not displaying on page details.
Merge branch '2.2/develop' into 2.2/fix_2
Changed to array_map
Merge pull request #2235 from jaminday/2.2/fix_2

Fixes issue #2228
Merge branch '2.2/develop' into 2.2/tprn