@Explain(displayName = "nullSafes")
  @Signature
  public String getNullSafeString() {
    if (nullsafes == null) {
      return null;
    }
    boolean hasNS = false;
    for (boolean ns : nullsafes) {
      hasNS |= ns;
    }
    return hasNS ? Arrays.toString(nullsafes) : null;
  }
@param skewKeysValuesTables
         set the table desc for storing skew keys and their corresponding
         value;
ql/src/java/org/apache/hadoop/hive/ql/plan/JoinDesc.java