Remove usage of _neitherNull on findProperty

[deblockt]

Remove usage of _neitherNull on findProperty to get custom property if possible.

linked issue : #1912

This PR is done for 2.9 version

[cowtowncoder]

(copied from older PR)

One other minor thing: I'm happy to merge this, but one thing we need before the first contribution to Jackson projects is CLA: (unless we already got one -- apologies if I missed earlier one, tried to check)

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

Usual way is to print, fill, sign, scan & email toinfo at fasterxml dot com.
There is also alternative Corporate CLA if you prefer, most contributions are under individual one.

[deblockt]

@cowtowncoder did you know when this bugfix will be released?

[cowtowncoder]

@deblockt Since 2.9.4 was just released, probably takes at least 1 month more. So perhaps late march or early april. There is no time-based release schedule but more of "when there are enough fixes bundled".