fix(wsgi): handle no root span (#2659) (#2669)

* fix(wsgi): handle no root span

It is possible for tracer.current_root_span() to return None which was
not handled here.

* Explicit none check

Co-authored-by: Julien Danjou <[email protected]>

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
Co-authored-by: Julien Danjou <[email protected]>
(cherry picked from commit 6f6da91)

Co-authored-by: Kyle Verhoog <[email protected]>

Author: mergify[bot]

ddtrace/contrib/wsgi/wsgi.py

@@ -97,9 +97,10 @@ def __init__(self, application, tracer=None, span_modifier=default_wsgi_span_mod
     def __call__(self, environ, start_response):
         def intercept_start_response(status, response_headers, exc_info=None):
             span = self.tracer.current_root_span()
-            status_code, status_msg = status.split(" ", 1)
-            span.set_tag("http.status_msg", status_msg)
-            trace_utils.set_http_meta(span, config.wsgi, status_code=status_code, response_headers=response_headers)
+            if span is not None:
+                status_code, status_msg = status.split(" ", 1)
+                span.set_tag("http.status_msg", status_msg)
+                trace_utils.set_http_meta(span, config.wsgi, status_code=status_code, response_headers=response_headers)
             with self.tracer.trace(
                 "wsgi.start_response",
                 service=trace_utils.int_service(None, config.wsgi),

releasenotes/notes/wsgi-73cf1d35043e7fef.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Fix a possible NoneType error in the WSGI middleware start_response method.