title: AttributeError: 'NoneType' object has no attribute 'app'
body: <p>The below code gives error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "pdf.py", line 14, in &lt;module&gt;
      create_pdf(render_template('templates.htm'))
    File "/usr/local/lib/python2.7/dist-packages/flask/templating.py", line 123, in render_template
      ctx.app.update_template_context(context)
  AttributeError: 'NoneType' object has no attribute 'app'
  </code></pre>
  
  <p>Code:</p>
  
  <pre><code>from xhtml2pdf import pisa
  from StringIO import StringIO
  from flask import render_template,Flask
  
  app=Flask(__name__)
  app.debug=True
  
  @app.route("/")
  def create_pdf(pdf_data):
          filename= "file.pdf"
          pdf=pisa.CreatePDF( StringIO(pdf_data),file(filename, "wb"))
  
  if __name__ == "__main__":
          create_pdf(render_template('templates.htm'))
  </code></pre>