public TruthValue or(TruthValue right) {
      if (right == null || right == this) {
        return this;
      }
      if (right == YES || this == YES) {
        return YES;
      }
      if (right == YES_NULL || this == YES_NULL) {
        return YES_NULL;
      }
      if (right == NO) {
        return this;
      }
      if (this == NO) {
        return right;
      }
      if (this == NULL) {
        if (right == NO_NULL) {
          return NULL;
        } else {
          return YES_NULL;
        }
      }
      if (right == NULL) {
        if (this == NO_NULL) {
          return NULL;
        } else {
          return YES_NULL;
        }
      }
      return YES_NO_NULL;
    }
Compute logical or between the two values.
@param right the other argument or null
@return the result
storage-api/src/java/org/apache/hadoop/hive/ql/io/sarg/SearchArgument.java