Last week I ran into some confusion when trying to use a FieldName is not null expression. See ArcGIS Pro Select By Attribute IS NOT NULL .
There were a number of records that had the string '<Null>' entered as the value which threw me off my game considerably. I talked to the data owner and he jumped on the problem immediately making the proper corrections.
Today I looked at the data again: it's a feature layer that is published from an enterprise geodatabase feature class to our local portal: the data owner made the edits to the e-gdb feature class. Now when I look at the data via the Select by Attribute tool in Pro, I still see <Null> listed as a value. The expression:
Reach ID is Equal to <Null> fails as it should
while Reach ID Is Null works, as it should
and Reach ID Is Not Null works as it should
However I still see an issue with the way Pro displays string field values with out quotes: the list displays <Null> as a valid value. After last week's foray, I still would consider this a six character string. ( <,N,u,l,l,>), but it isn't.