Handle missing __DEFAULT__ branch gracefully

There are cases that we don't want to do PR for patches without a mapped
branch. IOW, there is no "__DEFAULT__" branch. Handle such cases
gracefully.

Signed-off-by: Song Liu <[email protected]>

kernel_patches_daemon/github_sync.py

@@ -119,7 +119,7 @@ async def get_mapped_branches(self, series: Series) -> List[str]:
                 logging.info(f"Tag '{tag}' mapped to branch order {mapped_branches}")
                 return mapped_branches
 
-        mapped_branches = self.tag_to_branch_mapping["__DEFAULT__"]
+        mapped_branches = self.tag_to_branch_mapping.get("__DEFAULT__", [])
         logging.info(f"Mapped to default branch order: {mapped_branches}")
         return mapped_branches
 
@@ -199,6 +199,11 @@ async def sync_patches(self) -> None:
 
             mapped_branches = await self.get_mapped_branches(series)
             # series to apply - last known series
+            if len(mapped_branches) == 0:
+                logging.info(
+                    f"Skipping {series.id}: {subject.subject} for no mapped branches."
+                )
+                continue
             last_branch = mapped_branches[-1]
             for branch in mapped_branches:
                 worker = self.workers[branch]