diff --git a/lib/gitlab/ci/config/node/configurable.rb b/lib/gitlab/ci/config/node/configurable.rb
index 36d7d20c110..29de2d7d0b5 100644
--- a/lib/gitlab/ci/config/node/configurable.rb
+++ b/lib/gitlab/ci/config/node/configurable.rb
@@ -51,7 +51,7 @@ module Gitlab
             def helpers(*nodes)
               nodes.each do |symbol|
                 define_method("#{symbol}_defined?") do
-                  @entries[symbol].try(:defined?)
+                  @entries[symbol].specified?
                 end
 
                 define_method("#{symbol}_value") do
diff --git a/lib/gitlab/ci/config/node/entry.rb b/lib/gitlab/ci/config/node/entry.rb
index 02e4f7693da..c95e85200d2 100644
--- a/lib/gitlab/ci/config/node/entry.rb
+++ b/lib/gitlab/ci/config/node/entry.rb
@@ -66,14 +66,14 @@ module Gitlab
               @config
             else
               meaningful = @entries.select do |_key, value|
-                value.defined? && value.relevant?
+                value.specified? && value.relevant?
               end
 
               Hash[meaningful.map { |key, entry| [key, entry.value] }]
             end
           end
 
-          def defined?
+          def specified?
             true
           end
 
diff --git a/lib/gitlab/ci/config/node/factory.rb b/lib/gitlab/ci/config/node/factory.rb
index 3488aec4a22..602660acb93 100644
--- a/lib/gitlab/ci/config/node/factory.rb
+++ b/lib/gitlab/ci/config/node/factory.rb
@@ -40,11 +40,21 @@ module Gitlab
             # See issue #18775.
             #
             if @value.nil?
-              Node::Undefined.new(@node, attributes)
+              Node::Undefined.new(fabricate_undefined(attributes))
             else
               @node.new(@value, attributes)
             end
           end
+
+          private
+
+          def fabricate_undefined(attributes)
+            if @node.default.nil?
+              Node::Null.new(nil, attributes)
+            else
+              @node.new(@node.default, attributes)
+            end
+          end
         end
       end
     end
diff --git a/lib/gitlab/ci/config/node/null.rb b/lib/gitlab/ci/config/node/null.rb
index c7bbc16939a..880d29f663d 100644
--- a/lib/gitlab/ci/config/node/null.rb
+++ b/lib/gitlab/ci/config/node/null.rb
@@ -8,10 +8,6 @@ module Gitlab
         # Implements the Null Object pattern.
         #
         class Null < Entry
-          def initialize(config = nil, **attributes)
-            super
-          end
-
           def value
             nil
           end
@@ -23,6 +19,14 @@ module Gitlab
           def errors
             []
           end
+
+          def specified?
+            false
+          end
+
+          def relevant?
+            false
+          end
         end
       end
     end
diff --git a/lib/gitlab/ci/config/node/undefined.rb b/lib/gitlab/ci/config/node/undefined.rb
index fedb9d020be..384774c9b69 100644
--- a/lib/gitlab/ci/config/node/undefined.rb
+++ b/lib/gitlab/ci/config/node/undefined.rb
@@ -3,66 +3,19 @@ module Gitlab
     class Config
       module Node
         ##
-        # This class represents an undefined entry node.
+        # This class represents an undefined and unspecified entry node.
         #
-        # It takes original entry class as configuration and creates an object
-        # if original entry has a default value. If there is default value
-        # some methods are delegated to it.
+        # It decorates original entry adding method that idicates it is
+        # unspecified.
         #
-        #
-        class Undefined < Entry
-          include Validatable
-
-          delegate :valid?, :errors, :value, to: :@strategy
-
-          validations do
-            validates :config, type: Class
-          end
-
-          def initialize(node, **attributes)
+        class Undefined < SimpleDelegator
+          def initialize(entry)
             super
-            @strategy = create_strategy(node, node.default)
           end
 
-          def defined?
+          def specified?
             false
           end
-
-          private
-
-          def create_strategy(node, default)
-            if default.nil?
-              Undefined::NullStrategy.new
-            else
-              entry = node.new(default, attributes)
-              Undefined::DefaultStrategy.new(entry)
-            end
-          end
-
-          class DefaultStrategy
-            delegate :valid?, :errors, :value, to: :@default
-
-            def initialize(entry)
-              @default = entry
-            end
-          end
-
-          class NullStrategy
-            def initialize(*)
-            end
-
-            def value
-              nil
-            end
-
-            def valid?
-              true
-            end
-
-            def errors
-              []
-            end
-          end
         end
       end
     end
diff --git a/spec/lib/gitlab/ci/config/node/global_spec.rb b/spec/lib/gitlab/ci/config/node/global_spec.rb
index 786fc5bb6ce..1945b0326cc 100644
--- a/spec/lib/gitlab/ci/config/node/global_spec.rb
+++ b/spec/lib/gitlab/ci/config/node/global_spec.rb
@@ -233,9 +233,9 @@ describe Gitlab::Ci::Config::Node::Global do
     end
   end
 
-  describe '#defined?' do
+  describe '#specified?' do
     it 'is concrete entry that is defined' do
-      expect(global.defined?).to be true
+      expect(global.specified?).to be true
     end
   end
 end
diff --git a/spec/lib/gitlab/ci/config/node/null_spec.rb b/spec/lib/gitlab/ci/config/node/null_spec.rb
index 63b23ed0bd1..1ab5478dcfa 100644
--- a/spec/lib/gitlab/ci/config/node/null_spec.rb
+++ b/spec/lib/gitlab/ci/config/node/null_spec.rb
@@ -1,7 +1,7 @@
 require 'spec_helper'
 
 describe Gitlab::Ci::Config::Node::Null do
-  let(:null) { described_class.new }
+  let(:null) { described_class.new(nil) }
 
   describe '#leaf?' do
     it 'is leaf node' do
@@ -26,4 +26,16 @@ describe Gitlab::Ci::Config::Node::Null do
       expect(null.value).to eq nil
     end
   end
+
+  describe '#relevant?' do
+    it 'is not relevant' do
+      expect(null.relevant?).to eq false
+    end
+  end
+
+  describe '#specified?' do
+    it 'is not defined' do
+      expect(null.specified?).to eq false
+    end
+  end
 end
diff --git a/spec/lib/gitlab/ci/config/node/undefined_spec.rb b/spec/lib/gitlab/ci/config/node/undefined_spec.rb
index 417b4a0ad6f..2d43e1c1a9d 100644
--- a/spec/lib/gitlab/ci/config/node/undefined_spec.rb
+++ b/spec/lib/gitlab/ci/config/node/undefined_spec.rb
@@ -4,66 +4,29 @@ describe Gitlab::Ci::Config::Node::Undefined do
   let(:undefined) { described_class.new(entry) }
   let(:entry) { spy('Entry') }
 
-  context 'when entry does not have a default value' do
-    before { allow(entry).to receive(:default).and_return(nil) }
-
-    describe '#leaf?' do
-      it 'is leaf node' do
-        expect(undefined).to be_leaf
-      end
-    end
-
-    describe '#valid?' do
-      it 'is always valid' do
-        expect(undefined).to be_valid
-      end
-    end
-
-    describe '#errors' do
-      it 'is does not contain errors' do
-        expect(undefined.errors).to be_empty
-      end
-    end
-
-    describe '#value' do
-      it 'returns nil' do
-        expect(undefined.value).to eq nil
-      end
+  describe '#valid?' do
+    it 'delegates method to entry' do
+      expect(undefined.valid).to eq entry
     end
   end
 
-  context 'when entry has a default value' do
-    before do
-      allow(entry).to receive(:default).and_return('some value')
-      allow(entry).to receive(:value).and_return('some value')
-    end
-
-    describe '#value' do
-      it 'returns default value for entry' do
-        expect(undefined.value).to eq 'some value'
-      end
-    end
-
-    describe '#errors' do
-      it 'delegates errors to default entry' do
-        expect(entry).to receive(:errors)
-
-        undefined.errors
-      end
-    end
-
-    describe '#valid?' do
-      it 'delegates valid? to default entry' do
-        expect(entry).to receive(:valid?)
-
-        undefined.valid?
-      end
+  describe '#errors' do
+    it 'delegates method to entry' do
+      expect(undefined.errors).to eq entry
     end
   end
 
-  describe '#undefined?' do
-    it 'is not a defined entry' do
-      expect(undefined.defined?).to be false
+  describe '#value' do
+    it 'delegates method to entry' do
+      expect(undefined.value).to eq entry
+    end
+  end
+
+  describe '#specified?' do
+    it 'is always false' do
+      allow(entry).to receive(:specified?).and_return(true)
+
+      expect(undefined.specified?).to be false
     end
   end
 end