ref: Clean up get_active_propagation_context (#5217)

### Description

No longer returns `None` since the last `isolation_scope` branch will
always have one setup by the constructor.

#### Issues

* resolves: #5216 
* resolves: PY-2011

Author: sl0thentr0py

sentry_sdk/scope.py

@@ -45,7 +45,7 @@
 )
 
 import typing
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, cast
 
 if TYPE_CHECKING:
     from collections.abc import Mapping
@@ -546,12 +546,7 @@ def get_traceparent(self, *args, **kwargs):
             return self.span.to_traceparent()
 
         # else return traceparent from the propagation context
-        propagation_context = self.get_active_propagation_context()
-        if propagation_context is not None:
-            return propagation_context.to_traceparent()
-
-        # TODO-neel will never happen
-        return None
+        return self.get_active_propagation_context().to_traceparent()
 
     def get_baggage(self, *args, **kwargs):
         # type: (Any, Any) -> Optional[Baggage]
@@ -566,12 +561,7 @@ def get_baggage(self, *args, **kwargs):
             return self.span.to_baggage()
 
         # else return baggage from the propagation context
-        propagation_context = self.get_active_propagation_context()
-        if propagation_context is not None:
-            return propagation_context.get_baggage()
-
-        # TODO-neel will never happen
-        return None
+        return self.get_active_propagation_context().get_baggage()
 
     def get_trace_context(self):
         # type: () -> Dict[str, Any]
@@ -588,8 +578,6 @@ def get_trace_context(self):
             return {"trace_id": trace_id, "span_id": span_id}
 
         propagation_context = self.get_active_propagation_context()
-        if propagation_context is None:
-            return {}
 
         return {
             "trace_id": propagation_context.trace_id,
@@ -650,13 +638,11 @@ def iter_trace_propagation_headers(self, *args, **kwargs):
             for header in span.iter_headers():
                 yield header
         else:
-            propagation_context = self.get_active_propagation_context()
-            if propagation_context is not None:
-                for header in propagation_context.iter_headers():
-                    yield header
+            for header in self.get_active_propagation_context().iter_headers():
+                yield header
 
     def get_active_propagation_context(self):
-        # type: () -> Optional[PropagationContext]
+        # type: () -> PropagationContext
         if self._propagation_context is not None:
             return self._propagation_context
 
@@ -665,10 +651,10 @@ def get_active_propagation_context(self):
             return current_scope._propagation_context
 
         isolation_scope = self.get_isolation_scope()
-        if isolation_scope._propagation_context is not None:
-            return isolation_scope._propagation_context
-
-        return None
+        # should actually never happen, but just in case someone calls scope.clear
+        if isolation_scope._propagation_context is None:
+            isolation_scope._propagation_context = PropagationContext()
+        return isolation_scope._propagation_context
 
     def clear(self):
         # type: () -> None
@@ -1057,10 +1043,11 @@ def start_transaction(
         # update the sample rate in the dsc
         if transaction.sample_rate is not None:
             propagation_context = self.get_active_propagation_context()
-            if propagation_context:
-                baggage = propagation_context.baggage
-                if baggage is not None:
-                    baggage.sentry_items["sample_rate"] = str(transaction.sample_rate)
+            baggage = propagation_context.baggage
+
+            if baggage is not None:
+                baggage.sentry_items["sample_rate"] = str(transaction.sample_rate)
+
             if transaction._baggage:
                 transaction._baggage.sentry_items["sample_rate"] = str(
                     transaction.sample_rate
@@ -1134,8 +1121,7 @@ def start_span(self, instrumenter=INSTRUMENTER.SENTRY, **kwargs):
                 # New spans get the `trace_id` from the scope
                 if "trace_id" not in kwargs:
                     propagation_context = self.get_active_propagation_context()
-                    if propagation_context is not None:
-                        kwargs["trace_id"] = propagation_context.trace_id
+                    kwargs["trace_id"] = propagation_context.trace_id
 
                 span = Span(**kwargs)
             else:
@@ -1154,7 +1140,7 @@ def continue_trace(
         self.generate_propagation_context(environ_or_headers)
 
         # generate_propagation_context ensures that the propagation_context is not None.
-        propagation_context = typing.cast(PropagationContext, self._propagation_context)
+        propagation_context = cast(PropagationContext, self._propagation_context)
 
         optional_kwargs = {}
         if name: