Fix NoMethodError when "qop" is not present

Author: nobu

lib/net/imap/authenticators/digest_md5.rb

@@ -26,7 +26,7 @@ def process(challenge)
         sparams[k] = v
       end
 
-      raise Net::IMAP::DataFormatError, "Bad Challenge: '#{challenge}'" unless c.eos?
+      raise Net::IMAP::DataFormatError, "Bad Challenge: '#{challenge}'" unless c.eos? and sparams['qop']
       raise Net::IMAP::Error, "Server does not support auth (qop = #{sparams['qop'].join(',')})" unless sparams['qop'].include?("auth")
 
       response = {

test/net/imap/test_imap_authenticators.rb

@@ -146,4 +146,11 @@ def test_digest_md5_authenticator_garbage
       auth.process('.')
     end
   end
+
+  def test_digest_md5_authenticator_no_qop
+    auth = digest_md5("user", "pass")
+    assert_raise(Net::IMAP::DataFormatError) do
+      auth.process('Qop=""')
+    end
+  end
 end