I created a table

Code:
CREATE TABLE basket (id INT NOT NULL AUTO_INCREMENT, item VARCHAR(50) NOT NULL, amount VARCHAR(50) NOT NULL);
and try to create an insert function:

Code:
public function add_basket_item() {
	include '../vo/basketVO.php';
		$stmt = mysqli_prepare($this->connection, "INSERT INTO basket (item, amount) VALUES (?, ?)");
		$this->throwExceptionOnError();

		mysqli_stmt_bind_param($stmt, 'ss',$item->item, $item->amount);
		$this->throwExceptionOnError();

		mysqli_stmt_execute($stmt);		
		$this->throwExceptionOnError();

		$autoid = mysqli_stmt_insert_id($stmt);

		mysqli_stmt_free_result($stmt);		
		mysqli_close($this->connection);

		return $autoid;
	}
But when I try to test the operation in Flex Builder I get the following error:

InvocationTargetException:There was an error while invoking the operation. Check your server settings and try invoking the operation again.
Reason: Server error MySQL Error - 1048: Column 'item' cannot be null /../services/DBBase.php on line 26

I have tried various things but just can't get it to work. Any help would be much appreciated.