public function NullComparisonExpression()
{
if ($this->_lexer->isNextToken(Lexer::T_INPUT_PARAMETER)) {
$this->match(Lexer::T_INPUT_PARAMETER);
$expr = new AST\InputParameter($this->_lexer->token['value']);
} else {
$expr = $this->SingleValuedPathExpression();
}
$nullCompExpr = new AST\NullComparisonExpression($expr);
$this->match(Lexer::T_IS);
if ($this->_lexer->isNextToken(Lexer::T_NOT)) {
$this->match(Lexer::T_NOT);
$nullCompExpr->not = true;
}
$this->match(Lexer::T_NULL);
return $nullCompExpr;
}