LP:736780 - BETWEEN with datetime + NULL does not return NULL in 5.1-micro

Not repeatable in mysql-5.1. In 5.1-micro, BETWEEN expressions that contain a datetime and NULL do not return NULL. Instead, they return FALSE, which is incorrect.

To repeat:

MySQL [test]> SELECT NOW() BETWEEN NULL AND '2011-01-01' ;
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1 row in set (0.01 sec)

should have returned NULL