panic: nil dereference in EXCLUDE clause's error message

Input to EXCLUDE expression is a string.

The string is split on ',' . Substrings are then Parsed() to give us a n1ql expression. 

for eg:

EXCLUDE "a ,b"

"a" -> `a` field

"b" -> `b` field

the case here is that the substring is parsed as a statement instead of an expression.

eg: EXCLUDE "SELECT 1"

hence we end up with a nil variable after type assertion to "Expression".