SPARK-6878 [CORE] Fix for sum on empty RDD fails with exception

Author: Erik van Oosten <evanoosten@ebay.com>

Closes #5489 from erikvanoosten/master and squashes the following commits:

1c91954 [Erik van Oosten] Rewrote double range matcher to an exact equality assert (SPARK-6878)
f1708c9 [Erik van Oosten] Fix for sum on empty RDD fails with exception (SPARK-6878)