check that context.sampling_priority is None, not just is

ddtrace/_trace/processor/__init__.py

@@ -152,7 +152,7 @@ def process_trace(self, trace):
             root_ctx = chunk_root._context
 
             # only sample if we haven't already sampled
-            if root_ctx and not root_ctx.sampling_priority:
+            if root_ctx and root_ctx.sampling_priority is None:
                 self.sampler.sample(trace[0])
             # When stats computation is enabled in the tracer then we can
             # safely drop the traces.

ddtrace/_trace/tracer.py

@@ -322,7 +322,7 @@ def deregister_on_start_span(self, func: Callable) -> Callable:
 
     def sample_before_fork(self) -> None:
         span = self.current_root_span()
-        if span is not None and not span.context.sampling_priority:
+        if span is not None and span.context.sampling_priority is None:
             self._sampler.sample(span)
 
     @property

ddtrace/propagation/_database_monitoring.py

@@ -64,7 +64,7 @@ def __init__(
 
     def inject(self, dbspan, args, kwargs):
         # run sampling before injection to propagate correct sampling priority
-        if ddtrace.tracer._sampler and not dbspan.context.sampling_priority:
+        if ddtrace.tracer._sampler and dbspan.context.sampling_priority is None:
             ddtrace.tracer._sampler.sample(dbspan._local_root)
 
         dbm_comment = self._get_dbm_comment(dbspan)

ddtrace/propagation/http.py

@@ -957,7 +957,7 @@ def parent_call():
             else:
                 span = span._local_root
             if span is not None:
-                if not span.context.sampling_priority:
+                if span.context.sampling_priority is None:
                     ddtrace.tracer._sampler.sample(span._local_root)
         if PROPAGATION_STYLE_DATADOG in config._propagation_style_inject:
             _DatadogMultiHeader._inject(span_context, headers)