Support passing multiple --migrate-nullness option for java_api_library

Bug: 347751326
Test: m droid
Change-Id: I7702021348004b5f6d686d71ee566c5589dbc4f5
diff --git a/java/java.go b/java/java.go
index 08fb678..39d0223 100644
--- a/java/java.go
+++ b/java/java.go
@@ -2285,10 +2285,10 @@
 
 	al.stubsFlags(ctx, cmd, stubsDir)
 
-	migratingNullability := String(al.properties.Previous_api) != ""
-	if migratingNullability {
-		previousApi := android.PathForModuleSrc(ctx, String(al.properties.Previous_api))
-		cmd.FlagWithInput("--migrate-nullness ", previousApi)
+	previousApi := String(al.properties.Previous_api)
+	if previousApi != "" {
+		previousApiFiles := android.PathsForModuleSrc(ctx, []string{previousApi})
+		cmd.FlagForEachInput("--migrate-nullness ", previousApiFiles)
 	}
 
 	al.addValidation(ctx, cmd, al.validationPaths)