Mutable drops should fallback to their own methods when a mutation isn't present

lib/jekyll-github-metadata/metadata_drop.rb

@@ -11,11 +11,9 @@ class MetadataDrop < Jekyll::Drops::Drop
       # See https://github.com/jekyll/jekyll/pull/6338
       alias_method :invoke_drop, :[]
       def key?(key)
-        if self.class.mutable?
-          @mutations.key?(key)
-        else
-          !key.nil? && (respond_to?(key) || fallback_data.key?(key))
-        end
+        return false if key.nil?
+        return true if self.class.mutable? && @mutations.key?(key)
+        respond_to?(key) || fallback_data.key?(key)
       end
 
       def to_s

spec/metadata_drop_spec.rb

@@ -50,4 +50,53 @@
       expect(payload.keys).to match_array(expected_values.keys)
     end
   end
+
+  context "returning values" do
+    context "native methods" do
+      it "returns a value via #[]" do
+        expect(subject["url"]).to eql("http://jekyll.github.io/github-metadata")
+      end
+
+      it "returns a value via #invoke_drop" do
+        expect(subject.invoke_drop("url")).to eql("http://jekyll.github.io/github-metadata")
+      end
+
+      it "responds to #key?" do
+        expect(subject.key?("url")).to be_truthy
+      end
+    end
+
+    context "with mutated values" do
+      before { subject["url"] = "foo" }
+
+      it "returns the mutated value via #[]" do
+        expect(subject["url"]).to eql("foo")
+      end
+
+      it "returns the mutated  via #invoke_drop" do
+        expect(subject.invoke_drop("url")).to eql("foo")
+      end
+
+      it "responds to #key?" do
+        expect(subject.key?("url")).to be_truthy
+      end
+    end
+
+    context "with fallback data" do
+      let(:fallback_data) { { "foo" => "bar" } }
+      before { subject.instance_variable_set("@fallback_data", fallback_data) }
+
+      it "returns the mutated value via #[]" do
+        expect(subject["foo"]).to eql("bar")
+      end
+
+      it "returns the mutated  via #invoke_drop" do
+        expect(subject.invoke_drop("foo")).to eql("bar")
+      end
+
+      it "responds to #key?" do
+        expect(subject.key?("foo")).to be_truthy
+      end
+    end
+  end
 end