error adding location coordinates

[gswartz]

I have my schema set up with the following node....

 <field name="LocationCoordinates" type="location" indexed="true" stored="true" />

... and my class has the following property....

[SolrField("LocationCoordinates")]

public string LocationCoordinates

{

get

{

if (LocationZipCodeLat.HasValue && LocationZipCodeLon.HasValue)

{

var retval = LocationZipCodeLat.ToString() + "," + LocationZipCodeLon.ToString();

return retval;

}

return ",";

}

}

When LocationZipCodeLat and LocationZipCodeLon have a value I am able to add a document to my solr index.  However, when it gets to the else part which returns "," I get the following error in my log.  

SEVERE: org.apache.solr.common.SolrException: ERROR: [doc=827592] Error adding field 'LocationCoordinates'=','

at org.apache.solr.update.DocumentBuilder.toDocument(DocumentBuilder.java:333)

I've tried returning string.Empty also but I get the same error.  So, when I have an object without a location, what do I return from this property to be able to add the document?  Thanks.

[gswartz]

I think I've figured this out.  Rather than returning an empty string I need to return null.