title: Airborne::InvalidJsonError: Api request returned invalid json
body: <p>I'm getting below error while testing sample api in Airborne Ruby.</p>
  
  <blockquote>
    <p>Airborne::InvalidJsonError: Api request returned invalid json
     /Users/balamurugan/.rvm/gems/ruby-2.4.0/gems/airborne-0.2.13/lib/airborne/base.rb:73:in
    rescue in json_body
    /Users/balamurugan/.rvm/gems/ruby-2.4.0/gems/airborne-0.2.13/lib/airborne/base.rb:73:in
    json_body
    /Users/balamurugan/.rvm/gems/ruby-2.4.0/gems/airborne-0.2.13/lib/airborne/request_expectations.rb:139:in call_with_path
    /Users/balamurugan/.rvm/gems/ruby-2.4.0/gems/airborne-0.2.13/lib/airborne/request_expectations.rb:18:in expect_json ./postapinew_spec.rb:16:in block (2 levels) in '</p>
    
    <p>-e:1:in `load'</p>
    
    <p>-e:1:in `'</p>
    
    <hr>
    
    <p>--- Caused by: --- </p>
    
    <p>JSON::ParserError:   765: unexpected token at ''   /Users/balamurugan/.rvm/gems/ruby-2.4.0/gems/json-2.1.0/lib/json/common.rb:156:in
    `parse'</p>
  </blockquote>
  
  <h1>Code:</h1>
  
  <pre><code>require 'rspec'
  require 'airborne'
  require 'json'
  
  describe 'postapivalidation' do
  
    it 'should validate post api' do
      post 'http://localhost:9997/test',
           { 'Content-Type' =&gt; 'application/json' , 'Accept' =&gt; 'application/json' },
           { 'params' =&gt; {'param1' =&gt; 'value1' , 'param2' =&gt; 'value2' } }
      expect_status 200
      expect_json(name: 'Alex')
    end
  end
  </code></pre>
  
  <p>Issue is '<code>except_json</code>' related methods are not working for post <em>API</em>. But I got valid '<code>except_json</code>' results for get api. </p>
  
  <p>How to solve this issue???</p>