The fix for HADOOP-12590 left an unused import in TestCompressorDecompressor.java.
After uploading the patch for
HADOOP-12590, I spotted the problem in IntelliJ which marked the unused import gray, but it was too late.
The problem was not detected by precommit check because test source files are not checked by checkstyle by default. Maven checkstyle plugin parameter includeTestSourceDirectory is false by default.