The Iterate Row Selection tool does not honor null values besides the default value.
Last Published: April 21, 2016ArcGIS for Desktop
Bug ID Number
September 26, 2014
March 30, 2022
ArcGIS for Desktop
After review by the development team, it has been determined that this issue is related to a known limitation with the software that lies outside of Esri's control. The issue's Additional Information section may contain further explanation.
The null value indicates the output value used when a null value is detected in the field. It does not redefine what a null value is. If you do not want to include a value in the selection, use the Select Layer by Attribute tool to limit the featues that will be used.