yes, that's java. But I still can't figure out how to solve this problem :(

Hello, I have such an incomprehensible error: I passed all tests successfully, but I just can't pass the random test. For example, when I had an error, I wrote expected: <[a]> but was: <[]>. And in the case of a home test, it is written: (for example) expected: <AyEDW [cV]> but was: <AyEDW []>. If in a normal test <[]> what's inside is what I expect to get, then in the case of a random test I can't figure out what the text in front of the square brackets means? What is my mistake in this test?