KM VTS test fix - handled "null" value for imei.

Added a check to make sure IMEI is not "null".

Bug: 281676499
Test: atest VtsAidlKeyMintTargetTest
(cherry picked from https://android-review.googlesource.com/q/commit:71d19b21c30596b24ba053bfd9765528ee36901d)
Merged-In: Ia1569a30412d633eee4d4de8cd00dea077d1c23d
Change-Id: Ia1569a30412d633eee4d4de8cd00dea077d1c23d
1 file changed