In this case error out when no query is supplied. There seems to be an
infinite-loop casued by i think notmuch_query_search_threads having
an exception:

A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>
A Xapian exception occurred: Syntax: <expression> AND <expression>

I'll look into that bug specifically a bit later.

It might be better to do a usage instead of just throwing an error here?

alex