Adds to_nil! method with a bang

lib/to_nil.rb

@@ -1,10 +1,18 @@
 require "to_nil/version"
 
+# Errors
+require "to_nil/errors/could_not_nil"
+
 module ToNil
   module ObjectExtension
     def to_nil
       nil
     end
+
+    def to_nil!
+      self.to_nil == nil || raise(Errors::CouldNotNil.new("refused to nil", self))
+      nil
+    end
   end
 end
 

lib/to_nil/errors/could_not_nil.rb

@@ -0,0 +1,11 @@
+module ToNil
+  module Errors
+    class CouldNotNil < StandardError
+      attr_reader :object
+      def initialize(message, object)
+        super(message)
+        @object = object
+      end
+    end
+  end
+end

spec/to_nil_spec.rb

@@ -9,9 +9,22 @@
     it "returns nil for a #{klass} instance" do
       expect(klass.new.to_nil).to be_nil
     end
+
+    it "returns nil for a #{klass} instance with a bang" do
+      expect(klass.new.to_nil!).to be_nil
+    end
+
+    it "raises an error when #{klass} instance is not nil with a bang" do
+      allow_any_instance_of(klass).to receive(:to_nil).and_return('Not Nil!')
+      expect{klass.new.to_nil!}.to raise_error
+    end
   end
 
   it "returns nil for nil.to_nil" do
     expect(nil.to_nil).to be_nil
   end
+
+  it "returns nil for nil.to_nil with a bang" do
+    expect(nil.to_nil!).to be_nil
+  end
 end