Allow cookbooks to be defined with no source option in DSL

lib/chef-dk/policyfile/cookbook_location_specification.rb

@@ -80,7 +80,7 @@ def valid?
 
       def errors
         error_messages = []
-        if installer.nil?
+        if source_options_invalid?
           error_messages << "Cookbook `#{name}' has invalid source options `#{source_options.inspect}'"
         end
         error_messages
@@ -124,6 +124,10 @@ def source_options_for_lock
         installer.lock_data
       end
 
+      def source_options_invalid?
+        !source_options.empty? && installer.nil?
+      end
+
     end
   end
 end

spec/unit/policyfile_evaluation_spec.rb

@@ -206,6 +206,22 @@
 
         end
 
+        context "with an added cookbook with no options" do
+
+          let(:policyfile_rb) do
+            <<-EOH
+              run_list "foo", "bar"
+              cookbook "baz"
+            EOH
+          end
+
+          it "adds the cookbook to the list of location specs" do
+            expect(policyfile.errors).to eq([])
+            expected_cb_spec = ChefDK::Policyfile::CookbookLocationSpecification.new("baz", ">= 0.0.0", {}, storage_config)
+            expect(policyfile.cookbook_location_specs).to eq("baz" => expected_cb_spec)
+          end
+        end
+
       end
 
       context "with the default source set to a chef server" do