Add Ci config entry that implements Null Object

lib/gitlab/ci/config/node/entry.rb

@@ -5,22 +5,28 @@ module Gitlab
         class Entry
           include Config::ValidationHelpers
 
-          attr_reader :value, :parent
+          attr_reader :value, :nodes, :parent
 
           def initialize(value, config, parent = nil)
             @value = value
             @config = config
             @parent = parent
-            @nodes = {}
-            @errors = []
+            @nodes, @errors = [], []
+
+            keys.each_key do |key|
+              instance_variable_set("@#{key}", Null.new(nil, config, self))
+            end
           end
 
           def process!
             return if leaf?
 
-            keys.each_pair do |key, entry|
-              next unless @value.include?(key)
-              @nodes[key] = entry.new(@value[key], @config, self)
+            keys.each do |key, entry_class|
+              next unless @value.has_key?(key)
+
+              entry = entry_class.new(@value[key], @config, self)
+              instance_variable_set("@#{key}", entry)
+              @nodes.append(entry)
             end
 
             nodes.each(&:process!)
@@ -31,10 +37,6 @@ module Gitlab
             @errors + nodes.map(&:errors).flatten
           end
 
-          def nodes
-            @nodes.values
-          end
-
           def valid?
             errors.none?
           end

lib/gitlab/ci/config/node/null.rb

+module Gitlab
+  module Ci
+    class Config
+      module Node
+        class Null < Entry
+          def keys
+            {}
+          end
+
+          def method_missing(*)
+            nil
+          end
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/ci/config/node/null_spec.rb

+require 'spec_helper'
+
+describe Gitlab::Ci::Config::Node::Null do
+  let(:entry) { described_class.new(double, double) }
+
+  describe '#leaf?' do
+    it 'is leaf node' do
+      expect(entry).to be_leaf
+    end
+  end
+
+  describe '#any_method' do
+    it 'responds with nil' do
+      expect(entry.any_method).to be nil
+    end
+  end
+end