Takes two streams (fullStream and hashStream) and joins them similar to an LeftOuterJoinStream. The difference
in a OuterHashJoinStream is that the tuples in the hashStream will all be read and hashed when this stream is
opened. This provides a few optimizations iff the hashStream has a relatively small number of documents.
The difference between this and a HashJoinStream is that a tuple in the fullStream will be returned even
if it doesn't have any matching tuples in the hashStream.
You are expected to provide a set of fields for which the hash will be calculated from. If a tuple from the
hashStream does not contain a value (ie, null) for one of the fields the hash is being computed on then that
tuple will not be considered a match to anything. If a tuple from the fullStream does not contain a value (ie, null)
for one of the fields the hash is being computed on then that tuple will be returned without any joined tuples
from the hashStream