Prevent NPE by return empty list

Bug: 329502978
Test: atest ProxyAccessibilityServiceConnectionTest

Flag: EXEMPT simple bug fix
Change-Id: I93f876e324044311780fba6ebeeb53f174d5056b
(cherry picked from commit fbc3ca8ea7fe504f4f0a6743dfb4649eb59b960d)
2 files changed