LANG-1167: Add null filter to ReflectionToStringBuilder

[MarkDacek]

@chtompki
First attempt at this. In order to avoid a large refactor or breaking existing implementations, the boolean has to be a negative (isExcludeNullValues instead of appendNullValues).

[coveralls]

Coverage increased (+0.01%) to 94.559% when pulling e423b0b on MarkDacek:LANG-1167 into bf80b9e on apache:master.

[chtompki]

@PascalSchumacher - Do you think we should take this approach, or the approach you went after in LANG-1164.

[PascalSchumacher]

@chtompki Sorry for the delay, other open source projects and vacations interfered.

As the ToStringStyle implementations are singletons, I do not see a save way to use #209 as a basis for this pull request. Maybe I'm missing something?

I think #209 and this can coexists (as long as the naming is aligned).

@MarkDacek Thanks for creating this pull request. I think it would be great to have this feature in commons-lang. 👍

[HiAscend]

hello ,
on V3.8 V3.8.1 V3.9
when i use
ReflectionToStringBuilder.toString(student, ToStringStyle.JSON_STYLE)
return some like
{"id":666,"age":22,"name":"\u4E2D\u56FD","birthday":"Thu Jul 04 13:29:26 CST 2019","book":{"name":null}}
the student name is "中国" but now it is in unicode charset

however
on V3.7 it is ok
see：https://bbs.csdn.net/topics/392557654?page=1#post-404105720