...
** (FunctionClauseError) no function clause matching in IO.chardata_to_string/1    
    
    The following arguments were given to IO.chardata_to_string/1:
    
        # 1
        nil
    
    Attempted function clauses (showing 2 out of 2):
    
        def chardata_to_string(string) when is_binary(string)
        def chardata_to_string(list) when is_list(list)
    
    (elixir 1.10.3) lib/io.ex:572: IO.chardata_to_string/1
    (elixir 1.10.3) lib/file.ex:214: File.exists?/2
    lib/exvcr/task/runner.ex:17: anonymous fn/1 in ExVCR.Task.Runner.show_vcr_cassettes/1
    (elixir 1.10.3) lib/enum.ex:783: Enum."-each/2-lists^foreach/1-0-"/2
    (elixir 1.10.3) lib/enum.ex:783: Enum.each/2
    (mix 1.10.3) lib/mix/task.ex:330: Mix.Task.run_task/3
    (mix 1.10.3) lib/mix/cli.ex:82: Mix.CLI.run_task/2