Fix _as_string output to only show when format specified

[colings86]

Closes #10284

[jpountz]

Seeing the fix, it looks like we should either remove ValueFormatter.RAW or enforce valueFormatter to be non-null?

[colings86]

@jpountz Good point. I tend to agree. I had a look into removing ValueFormatter.RAW and I'm not sure that's the way to go since if we remove it we will end up just recreating what it is doing inside if (valueFormatter == null) statements which feels like a step backwards to me.

I also had a look at enforcing that the valueFormatter is not null. This should be ok providing that we are ok with using ValueFormatter.Raw in the case where we cannot determine the valueType for the field? (see here). WDYT?

[jpountz]

@colings86 It sounds good to me!

[colings86]

@jpountz is it worth applying the fix as is to 1.5.2, 1.6, and 2.0 and then work on a new PR to force the valueFormat to be non-null from 2.0 onwards? I am a bit worried about maintaining backwards compatibility if we force the ValueFormat to be non-null as there are a number of cases where we currently set the ValueFormat, ValueFormatter and/or ValueParser to null.

[jpountz]

@colings86 +1 I'm fine with merging this PR if we also commit to clean it up in 2.0.