Error: Nodes Cannot be Empty

Marcel Gruber

September 28, 2022

This edition of rare and silly errors is brought to you by LINQ:

Exception: System.ArgumentException
Message: nodes cannot be empty.
Parameter name: nodes
Source: Sitecore.ContentSearch.Linq
   at Sitecore.ContentSearch.Linq.Nodes.OrNode..ctor(QueryNode[] nodes)
   at Sitecore.ContentSearch.Linq.Parsing.ExpressionParser.VisitNonItemTypeEnumerableContainsMethod(MethodCallExpression methodCall, ConstantNode left, QueryNode right)
   at Sitecore.ContentSearch.Linq.Parsing.ExpressionParser.VisitBinary(BinaryExpression expression)
   at Sitecore.ContentSearch.Linq.Parsing.ExpressionParser.VisitBinary(BinaryExpression expression)
   at Sitecore.ContentSearch.Linq.Parsing.ExpressionParser.VisitBinary(BinaryExpression expression)
   at Sitecore.ContentSearch.Linq.Parsing.ExpressionParser.VisitBinary(BinaryExpression expression)
   at Sitecore.ContentSearch.Linq.Parsing.ExpressionParser.VisitWhereMethod(MethodCallExpression methodCall)
   at Sitecore.ContentSearch.Linq.Parsing.ExpressionParser.Parse(Expression expression)
   at Sitecore.ContentSearch.Linq.Parsing.GenericQueryable`2.GetQuery(Expression expression)
   at Sitecore.ContentSearch.Linq.Parsing.GenericQueryable`2.GetEnumerator()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)

The offending line was where Sitecore ContentSearch's GetQueryable was called:

using (var searchContext = QueryHelper.SearchIndex.CreateSearchContext())
{
    var results = searchContext
        .GetQueryable<MySearchResultItem>()
        .Where(query)
        .ToList();
}

Knowing that the problem wasn't actually there, I inspected the query that was built prior to calling GetQueryable:

var query = PredicateBuilder.True<MySearchResultItem>();
ID[] legacyTargets = GetLegacyItemTargets();
query = query.And(x => legacyTargets.Contains(x.ItemId));

Given that the error message said nodes are empty, the smoking gun was the "array contains x" operation. But it worked on all environments, except for one! Turns out, it's because the legacyTargets array WAS empty. This was due to a content delta between environments in which some items that were expected to be there... Weren't.

This situation is such a classic one in Sitecore. When fetching any information related to items, there will always be a chance that information is missing or different than you were expecting. Defensive programming pays dividends.

Keep on building,

Marcel