diff --git a/lib/jbuilder.rb b/lib/jbuilder.rb
index d1e3140..aa4bf46 100644
--- a/lib/jbuilder.rb
+++ b/lib/jbuilder.rb
@@ -32,7 +32,7 @@ def set!(key, value = BLANK, *args, &block)
       else
         # json.comments { ... }
         # { "comments": ... }
-        _scope{ yield self }
+        _merge_block(key){ yield self }
       end
     elsif args.empty?
       if ::Jbuilder === value
@@ -52,7 +52,7 @@ def set!(key, value = BLANK, *args, &block)
     else
       # json.author @post.creator, :name, :email_address
       # { "author": { "name": "David", "email_address": "david@loudthinking.com" } }
-      _scope{ extract! value, *args }
+      _merge_block(key){ extract! value, *args }
     end
 
     _set_value key, result
@@ -174,13 +174,15 @@ def child!
   #
   #   [1,2,3]
   def array!(collection = [], *attributes, &block)
-    @attributes = if block
+    array = if block
       _map_collection(collection, &block)
     elsif attributes.any?
       _map_collection(collection) { |element| extract! element, *attributes }
     else
       collection
     end
+
+    merge! array
   end
 
   # Extracts the mentioned attributes or hash elements from the passed object and turns them into attributes of the JSON.
@@ -230,12 +232,7 @@ def attributes!
 
   # Merges hash or array into current builder.
   def merge!(hash_or_array)
-    if ::Array === hash_or_array
-      @attributes = [] unless ::Array === @attributes
-      @attributes.concat hash_or_array
-    else
-      @attributes.update hash_or_array
-    end
+    @attributes = _merge_values(@attributes, hash_or_array)
   end
 
   # Encodes the current builder as JSON.
@@ -253,12 +250,29 @@ def _extract_method_values(object, *attributes)
     attributes.each{ |key| _set_value key, object.public_send(key) }
   end
 
+  def _merge_block(key, &block)
+    current_value = _read(key, {})
+    raise NullError.build(key) if current_value.nil?
+    value = _scope{ yield self }
+    value.nil? ? value : _merge_values(current_value, value)
+  end
+
+  def _read(key, default = nil)
+    @attributes.fetch(_key(key)){ default }
+  end
+
+  def _write(key, value)
+    @attributes[_key(key)] = value
+  end
+
+  def _key(key)
+    @key_formatter.format(key)
+  end
+
   def _set_value(key, value)
     raise NullError.build(key) if @attributes.nil?
     return if @ignore_nil && value.nil?
-
-    key = @key_formatter.format(key)
-    @attributes[key] = value
+    _write key, value
   end
 
   def _map_collection(collection)
@@ -281,6 +295,19 @@ def _scope
   def _mapable_arguments?(value, *args)
     value.respond_to?(:map)
   end
+
+  def _merge_values(attributes, hash_or_array)
+    attributes = attributes.dup
+
+    if ::Array === hash_or_array
+      attributes = [] unless ::Array === attributes
+      attributes.concat hash_or_array
+    else
+      attributes.update hash_or_array
+    end
+
+    attributes
+  end
 end
 
 require 'jbuilder/jbuilder_template' if defined?(ActionView::Template)
diff --git a/test/jbuilder_test.rb b/test/jbuilder_test.rb
index ddb1129..66b77fe 100644
--- a/test/jbuilder_test.rb
+++ b/test/jbuilder_test.rb
@@ -121,6 +121,42 @@ class JbuilderTest < ActiveSupport::TestCase
     assert_equal 32, result['author']['age']
   end
 
+  test 'blocks are additive' do
+    result = jbuild do |json|
+      json.author do
+        json.name 'David'
+      end
+
+      json.author do
+        json.age  32
+      end
+    end
+
+    assert_equal 'David', result['author']['name']
+    assert_equal 32, result['author']['age']
+  end
+
+  test 'blocks are additive via extract syntax' do
+    person = Person.new('Pavel', 27)
+
+    result = jbuild do |json|
+      json.author person, :age
+      json.author person, :name
+    end
+
+    assert_equal 'Pavel', result['author']['name']
+    assert_equal 27, result['author']['age']
+  end
+
+  test 'arrays are additive' do
+    result = jbuild do |json|
+      json.array! %w[foo]
+      json.array! %w[bar]
+    end
+
+    assert_equal %w[foo bar], result
+  end
+
   test 'nesting multiple children with block' do
     result = jbuild do |json|
       json.comments do
@@ -531,9 +567,40 @@ class JbuilderTest < ActiveSupport::TestCase
     assert_nil result
   end
 
-  test 'throws meaningfull error when on trying to add properties to null' do
+  test 'null! in a block' do
+    result = jbuild do |json|
+      json.author do
+        json.name 'David'
+      end
+
+      json.author do
+        json.null!
+      end
+    end
+
+    assert result.key?('author')
+    assert_nil result['author']
+  end
+
+  test 'throws NullError when trying to add properties to null' do
     json = Jbuilder.new
     json.null!
-    assert_raise(Jbuilder::NullError) { json.foo 'bar' }
+    assert_raise Jbuilder::NullError do
+      json.foo 'bar'
+    end
+  end
+
+  test 'throws NullError when trying to add properties to null using block syntax' do
+    assert_raise Jbuilder::NullError do
+      jbuild do |json|
+        json.author do
+          json.null!
+        end
+
+        json.author do
+          json.name "Pavel"
+        end
+      end
+    end
   end
 end