Fix issue with nil properties not being set and passing hash with string keys issue

lib/dolly/property_manager.rb

@@ -17,14 +17,14 @@ def update_attribute
       end
     end
 
-    def write_attribute key, value
+    def write_attribute(key, value)
       value = set_property_value(key, value)
       instance_variable_set(:"@#{key}", value)
-      update_doc(key, value) unless value.nil?
+      update_doc(key, value)
     end
 
     def valid_property?(name)
-      properties.include? name
+      properties.include?(name)
     end
 
     def update_doc(key, value)

test/property_manager_test.rb

@@ -0,0 +1,18 @@
+require 'test_helper'
+
+class TestDoc < Dolly::Document
+  property :name, class_name: String
+  property :email, class_name: String
+  property :last_name, class_name: String
+end
+
+class PropertyManagerTest < Test::Unit::TestCase
+  test 'write_attribute with nil value' do
+    doc = TestDoc.new(name: 'name', last_name: nil, email: 'does not change')
+    assert_equal(doc.name, 'name')
+    doc.update_properties(name: nil)
+    assert_equal(doc.name, nil)
+    assert_equal(doc.last_name, nil)
+    assert_equal(doc.email, 'does not change')
+  end
+end