Add some error handling around frame processing (elastic#837)

* Add some error handling around frame processing

See https://discuss.elastic.co/t/python-agent-raise-valueerror/233263

* Add a log to make sure the user doesn't wonder where the frames are

* Use `break` instead of `continue`

* Add to changelog

CHANGELOG.asciidoc

@@ -28,6 +28,11 @@ endif::[]
  * capture number of affected rows for INSERT/UPDATE/DELETE SQL queries {pull}614[#614]
  * Added instrumentation for AsyncElasticsearch {pull}843[#843]
 
+[float]
+===== Bug fixes
+
+* Added error handling around frame processing in Django {pull}837[#837]
+
 
 [[release-notes-5.x]]
 === Python Agent version 5.x

elasticapm/contrib/django/utils.py

@@ -29,6 +29,8 @@
 #  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 
+import logging
+
 from django.template.base import Node
 
 from elasticapm.utils.stacks import get_frame_info
@@ -51,7 +53,13 @@ def iterate_with_template_sources(
     locals_processor_func=None,
 ):
     template = None
-    for frame, lineno in frames:
+    for f in frames:
+        try:
+            frame, lineno = f
+        except ValueError:
+            # TODO how can we possibly get anything besides a (frame, lineno) tuple here???
+            logging.getLogger("elasticapm").error("Malformed list of frames. Frames may be missing in Kibana.")
+            break
         f_code = getattr(frame, "f_code", None)
         if f_code:
             function_name = frame.f_code.co_name