Update util/opentelemetry-util-http/src/opentelemetry/util/http/__init__.py

Co-authored-by: Shalev Roda <[email protected]>

Author: adriangb

util/opentelemetry-util-http/src/opentelemetry/util/http/__init__.py

@@ -219,7 +219,7 @@ def sanitize_method(method: Optional[str]) -> Optional[str]:
 
 def get_custom_headers(env_var: str) -> list[str]:
     custom_headers = environ.get(env_var, None)
-    if custom_headers:
+    if custom_headers is not None:
         return [
             custom_headers.strip()
             for custom_headers in custom_headers.split(",")