SLD with the Interpolate function doesn't work if the column contains NULL values.
org.geoserver.platform.ServiceException: Rendering process failed
Attached is a zip containing an SLD and an edited version of the sample data states.shp (Texas' PERSONS attribute has been set to NULL).
The rendering works if the null values are excluded (either by SLD filter or CQL).
Windows Server 2008
One thing to check is the semantic of null handling... what value should be associated to a null (null -> null? null -> lowest?)?
The interpolate function is defined in the SLD 1.1 specification, someone should check if there is any direction there.