code: function hasInvalidUnitsFromHistory(conn, address, cb){
      var conn = conn || db;
      if(!validationUtils.isNonemptyString(address))
          return cb("param address is null or empty string");
      if(!validationUtils.isValidAddress(address))
          return cb("param address is not a valid address");
      conn.query(
          "SELECT address FROM units JOIN unit_authors USING(unit)  \n\
          WHERE is_stable=1 AND sequence!='good' AND address=?", 
          [address],
          function(rows){
              cb(null, rows.length > 0 ?  true : false);
          }
      );
  }
docs: Check if an address has sent invalid unit.
  
  @param	{obj}	    conn      if conn is null, use db query, otherwise use conn.
  @param	{string}	address
  @param	{function}	cb( err, hasInvalidUnits ) callback function
  If there's error, err is the error message and hasInvalidUnits is null.
  If there's no error and there's invalid units, then hasInvalidUnits is true, otherwise false.