TypeError in IS0401Test test_13
String indices must be integers on line 359 test_13, where stream_type is identified.

```
 * Running test_13
 * ERROR: string indices must be integers
192.168.200.43 - - [15/Jan/2019 11:36:20] "POST / HTTP/1.1" 500 -
Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/flask/app.py", line 2309, in __call__
    return self.wsgi_app(environ, start_response)
  File "/usr/local/lib/python3.5/dist-packages/flask/app.py", line 2295, in wsgi_app
    response = self.handle_exception(e)
  File "/usr/local/lib/python3.5/dist-packages/flask/app.py", line 1741, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python3.5/dist-packages/flask/_compat.py", line 35, in reraise
    raise value
  File "/usr/local/lib/python3.5/dist-packages/flask/app.py", line 2292, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.5/dist-packages/flask/app.py", line 1815, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python3.5/dist-packages/flask/app.py", line 1718, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python3.5/dist-packages/flask/_compat.py", line 35, in reraise
    raise value
  File "/usr/local/lib/python3.5/dist-packages/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python3.5/dist-packages/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/ipstudio-admin/nmos-testing/nmos-test.py", line 218, in index_page
    raise ex
  File "/home/ipstudio-admin/nmos-testing/nmos-test.py", line 215, in index_page
    result = test_obj.run_tests(test_selection)
  File "/home/ipstudio-admin/nmos-testing/GenericTest.py", line 133, in run_tests
    self.execute_tests(test_name)
  File "/home/ipstudio-admin/nmos-testing/GenericTest.py", line 101, in execute_tests
    self.result.append(method())
  File "/home/ipstudio-admin/nmos-testing/IS0401Test.py", line 359, in test_13
    stream_type = receiver["format"].split(":")[-1]
TypeError: string indices must be integers

```
diff --git a/IS0401Test.py b/IS0401Test.py
index af5ee5c..774e9ef 100644
--- a/IS0401Test.py
+++ b/IS0401Test.py
@@ -356,7 +356,11 @@ class IS0401Test(GenericTest):
         try:
             formats_tested = []
             for receiver in receivers.json():
-                stream_type = receiver["format"].split(":")[-1]
+                try:
+                    stream_type = receiver["format"].split(":")[-1]
+                except TypeError:
+                    return test.FAIL("Unexpected Receiver format: {}".format(receiver))
+
                 # Test each available receiver format once
                 if stream_type in formats_tested:
                     continue

['IS0401Test.py']