Populate row based on value in previous row, when new value encountered use that value for following rows. Currently trying AttributeManager

I'm doing this via PostGres table, but attached is a small example of some of my data in excel. Also attached are my transformers. I'm trying this via AttributeManager using an expression. Not sure if my syntax is just wrong or if my approach needs work also.

Question: When I encounter a null value I want to use the value from the previous row. I want to accomplish this for all rows until I hit a new value. Then when I hit that new value I want to use that new value in the null rows underneath it. I want to do this until the end of file. I have several thousand records like this. Reference the well_location column to see what I'm describing. Thanks for any help!