Broken parsing validation on double commas within arrays

[steffanmusokedd]

What:

When parsing an array with two consecutive commas, no parsing error is thrown. In this case we should expect a syntax error.

ex.

array = [1, 2, , 3, 4]

Potential issue:

Looks like there was a workaround for trailing commas that likely is root cause.
https://github.com/chimpler/pyhocon/blob/master/pyhocon/config_parser.py#L754-L764

[davlee1972]

See #232

There should be pre parsing checks that looks for consecutive commas and throws errors.

The post processing should not reject empty strings in arrays. Right now “” is getting tossed.