Filter Items for DropDown list based on SharePoint list
I have a Gallery linked to a SharePointList that I want to show, but I need this gallery to be filterable based on a multi-select dropdown. One column that I want to filter on is a text column that can be empty, so I have the following code to create a collection based on the column from the SharePoint list, and then filter that column down to only entries that are not blank, empty, or null. However this isn't working and I'm still getting the full list, which means the dropdown has empty values inserted into it.
Am I doing something wrong? This code is located in the OnVisible method of the screen the gallery and search box are contained in. I would also like to go further and only get distinct, non-empty values to display in the dropdown. Is this possible?