Cannot understand warnings in Gradient

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Background

I am now trying Gradual type checking, as a consequence I am giving a shot to Gradient. As I see it, this is an alternative to Dialyzer.

Problems

So, on my first ever code snippet, I started with a pure function:

defmodule TipCalculator do

  @spec getTipPercentage(List[String.t()]) :: non_neg_integer
  def getTipPercentage(names) do
    names_size = length(names)

    cond do
      names_size > 5 -> 20
      names_size > 0 -> 10
      true -> 0
    end
  end
end

From my point of view, my type checks are rather solid.
However, Gradient seems to have a different opinion:

===> Analyzing applications...
===> Compiling gradualizer
src/gradualizer.erl:45:2: Warning: opaque type top() is underspecified and therefore meaningless

src/typechecker.erl:3234:1: Warning: function type_check_cons_in/4 is unused
src/typechecker.erl:3247:1: Warning: function type_check_cons_union/4 is unused
src/typechecker.erl:4612:1: Warning: function verbose/3 is unused
src/typechecker.erl:4870:1: Warning: function gen_partition/3 is unused
src/typechecker.erl:4872:1: Warning: function paux/3 is unused

==> gradient
Compiling 14 files (.ex)
Generated gradient app
==> grokking_fp
Compiling 1 file (.ex)
warning: code block contains unused literal "\n" (remove the literal or assign it to _ to avoid warnings)
  lib/tip_calculator.ex: TipCalculator

Generated grokking_fp app
Typechecking files...
lib/tip_calculator.ex: Undefined remote type Access:get/2 on line 0

From what I can understand, this one piece of code (from a fresh project) has several issues:

  1. warning: code block contains unused literal “\n” (remove the literal or assign it to _ to avoid warnings)
  2. lib/tip_calculator.ex: Undefined remote type Access:get/2 on line 0

The fist one sounds like a warning credo (or a linter) would give me. So I am not really sure what do do with it. I am expecting a tool that does type checks only (maybe I am wrong?).

The second one, I have no idea.

Questions

What am I doing wrong?

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