Ruby soap4r-未初始化的常量REXML:：元素

我试图在我的rails项目（ruby版本1.9.3）中使用soap4r和jira4r

在我的档案中：

gem 'soap4r', :git => 'git://github.com/felipec/soap4r.git'
gem 'jira4r-jh'

当我尝试在我的模型中运行时

require "jira4r/jira-tool"

model Mymodel

  def mydef

    jira = Jira4R::JiraTool.new(2, "http://my.website.com/")
    jira.login("test@test.com","password")

  end
end

我得到一个错误：

uninitialized constant REXML::Element

rubyjedi-soap4r (1.5.8.01) lib/soap/mapping/mapping.rb:129:in `_obj2soap'
rubyjedi-soap4r (1.5.8.01) lib/soap/mapping/mapping.rb:54:in `block (2 levels) in objs2soap'
rubyjedi-soap4r (1.5.8.01) lib/soap/mapping/mapping.rb:52:in `upto'
rubyjedi-soap4r (1.5.8.01) lib/soap/mapping/mapping.rb:52:in `block in objs2soap'
rubyjedi-soap4r (1.5.8.01) lib/soap/mapping/mapping.rb:560:in `block in protect_mapping'
rubyjedi-soap4r (1.5.8.01) lib/soap/mapping/mapping.rb:533:in `protect_threadvars'
rubyjedi-soap4r (1.5.8.01) lib/soap/mapping/mapping.rb:549:in `protect_mapping'
rubyjedi-soap4r (1.5.8.01) lib/soap/mapping/mapping.rb:51:in `objs2soap'
rubyjedi-soap4r (1.5.8.01) lib/soap/rpc/proxy.rb:475:in `request_rpc_enc'
rubyjedi-soap4r (1.5.8.01) lib/soap/rpc/proxy.rb:457:in `request_rpc'
rubyjedi-soap4r (1.5.8.01) lib/soap/rpc/proxy.rb:412:in `request_body'
rubyjedi-soap4r (1.5.8.01) lib/soap/rpc/proxy.rb:127:in `call'
rubyjedi-soap4r (1.5.8.01) lib/soap/rpc/driver.rb:151:in `call'

但若我在独立的非rails ruby项目中运行相同的代码，它就会正常工作

如何修复它？

通过添加

require 'rexml/document'