Cryptic error when there is no issue in the given line

[adamniedzielski]

Thank you for an amazing piece of software! I have a bug to report:

Description

When you run:

mix credo lib/chapter_sampler.ex:6

and there is no issue in the given line, you will get quite a cryptic error:

Checking 1 source file ...
** (UndefinedFunctionError) undefined function nil.scope/0
    nil.scope()
    Credo.CLI.Output.Explain.print_issues/7
    lib/credo/cli/command/explain.ex:22: Credo.CLI.Command.Explain.run/2
    lib/credo/cli.ex:53: Credo.CLI.main/1
    (mix) lib/mix/cli.ex:58: Mix.CLI.run_task/2

Real life case

First I run mix credo --strict and it reported an issue in lib/chapter_sampler.ex:6. Then I wanted to get the details of this issue, but I didn't specify the --strict switch and I got the above error. The issue was one of these "strict" ones.

[rrrene]

Ah, very good! I mean, not "good" good, but a good error report 👍 😁