Android : ruby execute script function return null on android browser selenium

I have written a ruby script using selenium webdriver I am using Browserstack to test my script. it is running fine on windows(Chrome, firefox), OS X(chrome, frefox) but when I use android browser execute_script() function returns null here is my code

require 'rubygems'
require 'selenium-webdriver'
#input capabilities

caps = Selenium::WebDriver::Remote::Capabilities.new

caps['browser'] = 'android'
caps['os'] = 'android'
caps['device'] = 'Google Nexus'
caps['os_version'] = '4.2'

caps['name'] = 'Nestaway Android Device test'

driver = Selenium::WebDriver.for(:remote, :url => "http://rohitkumar19:toTFtkgPDnVJRkgtnCyP@hub.browserstack.com/wd/hub", :desired_capabilities => caps)

siteUrl = 'http://localhost:3000/'

driver.manage.timeouts.implicit_wait = 10

driver.navigate.to siteUrl

myscript = "var name = 'rohit kumar';
return name;"
result = driver.execute_script(myscript)

puts result

driver.quit

why this is happening. any suggestion please. Thanks in advance