public static boolean onExpressionHasNullSafes(JoinDesc desc) {
    boolean[] nullSafes = desc.getNullSafes();
    if (nullSafes == null) {
      return false;
    }
    for (boolean nullSafe : nullSafes) {
      if (nullSafe) {
        return true;
      }
    }
    return false;
  }
convert a regular join to a a map-side join.

@param op
         join operator
@param mapJoinPos
         position of the source to be read as part of map-reduce framework. All other sources
         are cached in memory
@param noCheckOuterJoin
@param validateMapJoinTree
ql/src/java/org/apache/hadoop/hive/ql/optimizer/MapJoinProcessor.java