code: public static Constant defaultInstance(Type type) {
  		switch (type.getSqlType()) {
  		case (INTEGER):
  			return defaultInteger;
  		case (BIGINT):
  			return defaultBigInt;
  		case (DOUBLE):
  			return defaultDouble;
  		case (VARCHAR):
  			return defaultVarchar;
  		}
  		throw new UnsupportedOperationException("Unspported SQL type: " + type.getSqlType());
  	}
docs: Constructs a new instance of the specified type with default value. For
  all numeric constants, the default value is 0; for string constants, the
  default value is an empty string.
  
  @param type
  the specified type
  @return the constant of specified type with default value