List supported authorites for selected accounts
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I'm trying to develop an application which sync only selected accounts using `ContentResolver.requestSync(account, authority, extras);`.
I was able to sync contacts and calendar by using `com.android.contacts` and `com.android.calendar` respectively as `authority`. But, is there any way to get the list of authorities supported by a specific account?
Also, what is the effect of using `null` as authority?