[BUG] --filter-by wrong section name throws exception

[frextrite]

Command Run

$ coala --json --filter-by some_unknown_filter_that_doesnt_exist

Output

[ERROR][14:47:33] An unknown error occurred. This is a bug. We are sorry for the inconvenience. Please contact the developers for assistance. During execution of coala an exception was raised. This should never happen. When asked for, the following information may help investigating:
[INFO][14:47:33] Exception was:
Traceback (most recent call last):

  File "/home/amol/GitHub/coala/coalib/coala_main.py", line 170, in run_coala
    filtered = apply_filters(filters, sections=all_sections)

  File "/home/amol/GitHub/coala/coalib/parsing/FilterHelper.py", line 81, in apply_filters
    items = applier(filter_name, filter_args, items)

  File "/home/amol/GitHub/coala/coalib/parsing/FilterHelper.py", line 101, in _apply_section_filter
    raise InvalidFilterException(filter_name)

coalib.parsing.InvalidFilterException.InvalidFilterException: 'some_unknown_filter_that_doesnt_exist' is an invalid filter. Available filters: can_detect, can_fix, language, section_tags


During handling of the above exception, another exception occurred:


Traceback (most recent call last):

  File "/home/amol/GitHub/coala/coalib/coala_main.py", line 174, in run_coala
    console_printer.print(ex)

AttributeError: 'NoneType' object has no attribute 'print'

{
  "results": {}
}

Possible Solution

The proper error message must be shown indicating such a filter doesn't exist instead of throwing a raw error message.

InvalidFilterException exception is being correctly emitted by the bear, just need to catch it and show an error message.

difficulty/low

[xurror]

I'll like to work on this

[PrasanthChettri]

Hi can I work on this ?