Verify the modular stub flags are subsets of the monolithic stub flags

Bug: 179354495
Test: m out/soong/hiddenapi/hiddenapi-stub-flags.txt
      - check that an error is reported if a modular stub-flags.csv file,
        i.e. one created by a fragment is not a subset of the monolithic
        file, e.g. because a signature in the modular file has different
        flags than it does in the monolithic or is not present there.
Change-Id: I46ebb495cb093a5e3abe7571c49933c845318549
diff --git a/scripts/hiddenapi/verify_overlaps.py b/scripts/hiddenapi/verify_overlaps.py
index c8e3879..bb0917e 100755
--- a/scripts/hiddenapi/verify_overlaps.py
+++ b/scripts/hiddenapi/verify_overlaps.py
@@ -47,9 +47,9 @@
             if signature in allFlagsBySignature:
                 allFlags = allFlagsBySignature.get(signature)
                 if allFlags != row:
-                    mismatchingSignatures.append((signature, row[None], allFlags[None]))
+                    mismatchingSignatures.append((signature, row.get(None, []), allFlags.get(None, [])))
             else:
-                mismatchingSignatures.append((signature, row[None], []))
+                mismatchingSignatures.append((signature, row.get(None, []), []))
 
 
     if mismatchingSignatures:
@@ -60,7 +60,7 @@
         for mismatch in mismatchingSignatures:
             print()
             print("< " + mismatch[0] + "," + ",".join(mismatch[1]))
-            if mismatch[2] != None:
+            if mismatch[2] != []:
                 print("> " + mismatch[0] + "," + ",".join(mismatch[2]))
             else:
                 print("> " + mismatch[0] + " - missing")