Added palette model gray and color defaults

Necessary to provide typed defaults when attributes are missing. This is especially important when the API answers `nil` values since the API doesn't provide safe defaults.

Milestone: minor

lib/trmnl/api/models/palette.rb

@@ -10,6 +10,13 @@ module TRMNL
         using Refinements::Hash
 
         def self.for(attributes) = new(**attributes.transform_keys(name: :label, id: :name))
+
+        def initialize(**)
+          super
+          self[:grays] ||= 0
+          self[:colors] ||= []
+          freeze
+        end
       end
     end
   end

spec/lib/trmnl/api/models/palette_spec.rb

@@ -3,9 +3,21 @@
 require "spec_helper"
 
 RSpec.describe TRMNL::API::Models::Palette do
+  subject(:model) { described_class.new }
+
+  let :attributes do
+    {
+      name: "test",
+      label: "Test",
+      grays: 2,
+      colors: %w[#000000 #FFFFFF],
+      framework_class: "screen--1bit"
+    }
+  end
+
   describe ".for" do
     it "answers record for attributes" do
-      attributes = {
+      api_attributes = {
         id: "test",
         name: "Test",
         grays: 2,
@@ -13,15 +25,21 @@ RSpec.describe TRMNL::API::Models::Palette do
         framework_class: "screen--1bit"
       }
 
-      expect(described_class.for(attributes)).to eq(
-        described_class[
-          name: "test",
-          label: "Test",
-          grays: 2,
-          colors: %w[#000000 #FFFFFF],
-          framework_class: "screen--1bit"
-        ]
-      )
+      expect(described_class.for(api_attributes)).to eq(described_class[**attributes])
+    end
+  end
+
+  describe "#initalize" do
+    it "answers default attributes" do
+      expect(model).to have_attributes(grays: 0, colors: [])
+    end
+
+    it "answers custom attributes" do
+      expect(described_class[**attributes]).to have_attributes(attributes)
+    end
+
+    it "is frozen" do
+      expect(model.frozen?).to be(true)
     end
   end
 end