version: add empty? method

Library/Homebrew/test/version_spec.rb

@@ -173,6 +173,16 @@
     expect(versions.sort_by { |v| described_class.create(v) }).to eq(versions)
   end
 
+  describe "#empty?" do
+    it "returns true if version is empty" do
+      expect(described_class.create("").empty?).to eq(true)
+    end
+
+    it "returns false if version is not empty" do
+      expect(described_class.create("1.2.3").empty?).to eq(false)
+    end
+  end
+
   specify "hash equality" do
     v1 = described_class.create("0.1.0")
     v2 = described_class.create("0.1.0")

Library/Homebrew/version.rb

@@ -429,6 +429,10 @@ def <=>(other)
   end
   alias eql? ==
 
+  def empty?
+    version.empty?
+  end
+
   def hash
     version.hash
   end