Parser.php

<?php

// ...

// Validate SingleValuedPathExpression (ie.: "product")
if (isset($this->queryComponents[$lookaheadValue]['metadata'])) {
    $expr = $this->SingleValuedPathExpression();
    break;
}

// Validating ResultVariable
if ( ! isset($this->queryComponents[$lookaheadValue]['resultVariable'])) {
    $this->semanticalError('Cannot add having condition on a non result variable.');
}

// ...