Running version: 1.5.1.17#dev
Python version: 2.7.17
Operating system: Linux-3.4.39-10407293-armv7l-with-libc
Command line: sqlmap.py -u *************************************************** --dbs
Technique: UNION
Back-end DBMS: MySQL (identified)

Traceback (most recent call last):
  File "sqlmap.py", line 216, in main
    start()
  File "lib/core/decorators.py", line 78, in _
    result = f(*args, **kwargs)
  File "lib/controller/controller.py", line 591, in start
    injection = checkSqlInjection(place, parameter, value)
  File "lib/controller/checks.py", line 712, in checkSqlInjection
    reqPayload, vector = unionTest(comment, place, parameter, value, prefix, suffix)
  File "lib/core/decorators.py", line 78, in _
    result = f(*args, **kwargs)
  File "lib/techniques/union/test.py", line 388, in unionTest
    validPayload, vector = _unionTestByCharBruteforce(comment, place, parameter, value, prefix, suffix)
  File "lib/techniques/union/test.py", line 322, in _unionTestByCharBruteforce
    count = _findUnionCharCount(comment, place, parameter, value, prefix, suffix, where)
  File "lib/techniques/union/test.py", line 172, in _findUnionCharCount
    kb.errorIsNone = popValue()
  File "lib/core/common.py", line 2703, in popValue
    return getCurrentThreadData().valueStack.pop()
IndexError: pop from empty list