title: Undefined strip for Hash with custom headers on Savon 2.1.0
body: <p>I'm having an exception when trying to build custom headers with Savon 2.1.0 for Authentication, here is the sample code to reproduce the issue, I'll appreciate any help on this subject.</p>
  
  <pre><code>require 'open-uri'
  require 'savon'
  
  headers = {
    'IvansWSAuthentication' =&gt; {
      'User' =&gt; 'my_user',
      'Password' =&gt; 'my_pass',
      'ClientId' =&gt; 'my_client_id'
    }
  }
  
  x12 = 'test'
  
  client = Savon.client(
    wsdl: 'https://limeservices.ivans.com/EligibilityOne.asmx?WSDL',
    headers: headers
  )
  
  request_params = {
    form270: x12
  }
  
  response = client.call(:send_commercial_eligibility_form_request, message: request_params)
  </code></pre>
  
  <hr>
  
  <p>This is the exception:</p>
  
  <pre><code>1.9.3-p392 :023 &gt;   response = client.call(:send_commercial_eligibility_form_request, message: request_params)
  D, [2013-03-05T23:02:30.647097 #11590] DEBUG -- : HTTPI GET request to limeservices.ivans.com (net_http)
  I, [2013-03-05T23:02:31.600016 #11590]  INFO -- : SOAP request: https://limeservices.ivans.com/EligibilityOne.asmx
  I, [2013-03-05T23:02:31.600157 #11590]  INFO -- : IvansWSAuthentication: {"User"=&gt;"my_user", "Password"=&gt;"my_pass", "ClientId"=&gt;"my_client_id"}, SOAPAction: "http://tempuri.org/SendCommercialEligibilityFormRequest", Content-Type: text/xml;charset=UTF-8, Content-Length: 389
  D, [2013-03-05T23:02:31.600206 #11590] DEBUG -- : &lt;?xml version="1.0" encoding="UTF-8"?&gt;&lt;env:Envelope xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tns="http://tempuri.org/" xmlns:env="http://schemas.xmlsoap.org/soap/envelope/"&gt;&lt;env:Body&gt;&lt;tns:SendCommercialEligibilityFormRequest&gt;&lt;tns:form270&gt;test&lt;/tns:form270&gt;&lt;/tns:SendCommercialEligibilityFormRequest&gt;&lt;/env:Body&gt;&lt;/env:Envelope&gt;
  D, [2013-03-05T23:02:31.600474 #11590] DEBUG -- : HTTPI POST request to limeservices.ivans.com (net_http)
  NoMethodError: undefined method `strip' for #&lt;Hash:0x007fb044365a50&gt;
      from /Users/rorra/.rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/net/http.rb:1435:in `block in initialize_http_header'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/utils.rb:451:in `block in each'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/utils.rb:450:in `each'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/utils.rb:450:in `each'
      from /Users/rorra/.rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/net/http.rb:1433:in `initialize_http_header'
      from /Users/rorra/.rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/net/http.rb:1862:in `initialize'
      from /Users/rorra/.rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/net/http.rb:2093:in `initialize'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/httpi-2.0.2/lib/httpi/adapter/net_http.rb:87:in `new'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/httpi-2.0.2/lib/httpi/adapter/net_http.rb:87:in `request_client'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/httpi-2.0.2/lib/httpi/adapter/net_http.rb:55:in `block in do_request'
      from /Users/rorra/.rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/net/http.rb:745:in `start'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/httpi-2.0.2/lib/httpi/adapter/net_http.rb:54:in `do_request'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/httpi-2.0.2/lib/httpi/adapter/net_http.rb:31:in `request'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/httpi-2.0.2/lib/httpi.rb:137:in `request'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/httpi-2.0.2/lib/httpi.rb:109:in `post'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/savon-2.1.0/lib/savon/operation.rb:59:in `call!'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/savon-2.1.0/lib/savon/operation.rb:48:in `call'
      from /Users/rorra/.rvm/gems/ruby-1.9.3-p392/gems/savon-2.1.0/lib/savon/client.rb:38:in `call'
      from (irb):23
      from /Users/rorra/.rvm/rubies/ruby-1.9.3-p392/bin/irb:16:in `&lt;main&gt;'1.9.3-p392 :024 &gt; 
  </code></pre>