Excluding NULL values in Delete Identical geoprocessing tool

[Anonymous User]

I am using the Delete Identical tool in model builder to remove identical features using unique values in a specific field. In that field there are a few NULL values that are getting deleted since they are technically duplicates. Is there a way to add an expression or something similar so that the Delete Identical tool ignores NULL values and doesn't delete them? 

[DanPatterson_Retired · Accepted solution]

You might have to add a pre-step to select by attributes those attributes that are not Null, then the delete identical tool.

I would use the find identical tool for testing first though

Find Identical—Data Management toolbox | ArcGIS Desktop 

[Anonymous User]

Thank you, I was over thinking this one and forgot about select by attributes. 

[DuncanHornby]

To compliment Dan's answer you should know that ALL geo-processing tools honour selections first. So by applying a selection to a layer that is how you can process a subset of data.