# Sitecore ContentSearch - Filtering by null and empty strings


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By default Sitecore will not save `null` and empty strings in your indexes as it wastes space.
 
However, you might need to do something like this:

```csharp
using (var context = ContentSearchManager.GetIndex("MyIndex").CreateSearchContext())
{
    var query = context.GetQueryable<SearchResultItem>().Where(x => x.Name != null);
    var results = query.GetResults();
}
```
 
But that will result in an exception:
 
`System.NotSupportedException: Comparison of null values is not supported.`
 
Comparing with an empty string will not throw an exception, but it won’t return the expected results either, as the query will be translated into `-MatchNoDocsQuery[] +*:*` (Lucence).
 
## Solution
 
Luckily there is a solution. It is possible to overwrite this functionality on a per field basis.
 
You can add a `nullValue` and `emptyString` parameter to the needed fields in your index configuration under the `<fieldNames hint="raw:AddFieldByFieldName">` section:

```xml
<field 
    fieldName="name" storageType="NO" indexType="TOKENIZED" 
    vectorType="NO" boost="1f" type="System.String" 
    nullValue="NULL" emptyString="EMPTY"
    settingType="Sitecore.ContentSearch.LuceneProvider.LuceneSearchFieldConfiguration,                    
                 Sitecore.ContentSearch.LuceneProvider" />
```
 
This will map nulls and empty strings to the string values `"NULL"` and `"EMPTY"` respectively. You will now be able to do queries on nulls and empty strings without getting exceptions and also get the expected results.
 
## Considerations
 
You should be aware that this will increase the size of your index slightly. In most cases I don’t think it will have any noticable impact.
 
You can read a little more about this subject in [Sitecore’s own post about it](https://doc.sitecore.net/sitecore%20experience%20platform/search%20development/queries%20for%20null%20or%20empty%20strings).
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