fix: if JsonObject serialized to None then return null_value instead of string_value

[o-aleks]

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[asthamohta]

hi @o-aleks, what is this PR for?

[o-aleks]

Hi @asthamohta,

There is a bug in _make_value_pb function.
If the value is an instance of JsonObject and it is None after serializing, then it should be translated to NULL_VALUE, but in the original code, it is a string.

My fix is:

def _make_value_pb(value):
    ...
    if isinstance(value, JsonObject):
        value = value.serialize()
        if value is None:
            return Value(null_value="NULL_VALUE")
        else:
            return Value(string_value=value)

Could you please check it and approve the PR?
Thank you.

[IlyaFaer]

Should be okay. There is an if statement upper in the method, which does the same for all the data types, but JsonObject is more complicated than other types, so it passes the condition (and we can't change this behavior for the class, because there is no magic method for is None statements).

A test should be added though. @o-aleks, will you find time to add a test? Or I can do it in a separate issue.

[o-aleks]

A test should be added though. @o-aleks, will you find time to add a test? Or I can do it in a separate issue.
Oh, yes, of course, I'll add the test.

[IlyaFaer]

Thanks, @o-aleks, looks good, and tests are passing fine. I'm merging it.