// Single element
if (collectionExpression == null) {
addProblem(expression, ConcatExpression_MissingExpression);
}
else {
for (Expression child : collectionExpression.children()) {
if (!isValid(child, expression.getEncapsulatedExpressionQueryBNFId())) {
addProblem(child, ConcatExpression_InvalidExpression, child.toParsedText());
}
}
}