code: function getSupernodeByDepositAddress(conn, depositAddress, cb){
      var conn = conn || db;
      if(!validationUtils.isNonemptyString(depositAddress))
          return cb("param depostiAddress is null or empty string");
      if(!validationUtils.isValidAddress(depositAddress))
          return cb("param depostiAddress is not a valid address");
  
      conn.query("SELECT address, safe_address FROM supernode WHERE deposit_address = ?", [depositAddress], 
          function(rows) {
              if (rows.length !== 1 )
                  return cb("supernodeAddress is not found");
              cb(null, rows);
      });
  }
docs: Returns supernode address by deposit address.
  
  @param	{obj}	    conn      if conn is null, use db query, otherwise use conn.
  @param   {String}    depositAddress
  @param   {function}	cb( err, supernodeAddress ) callback function
  If depositAddress is invalid, then returns err "invalid address".
  If can not find the address, then returns err "supernodeAddress not found".