Merge "hidl_string: empty string opt always applies" am: 34fb6e1222 am: 2f35293174 am: 47b900270c

Original change: https://android-review.googlesource.com/c/platform/system/libhidl/+/1656230

Change-Id: I77bfb1ad910b1774e6fca27daabb522e7d9ea424