TAJO-833
TAJO-833: NPE occurs when using the column as a alias name in the multiple DISTINCT. (Hyoungjun Kim via hyunsik)

Closes #11
TAJO-832: NPE occurs when Exception's message is null in Task. (Hyoungjun Kim via hyunsik)
TAJO-827: SUM() overflow in the case of INT4. (Hyoungjun Kim via hyunsik)
TAJO-808: Fix pre-commit build failure. (jinho)