How to Create a 1:many relationship when null values are involved in a fact table

Hi there,

First time poster and beginner to Power Bi. I have a look up table with a column for a list of companies which I want to create a relationship with a column for companies in a fact table. There were nulls in the look up table which I removed through the Query Editor by filling down into those cells, and then removing duplicates. Within rows of the fact table and its company column there are null values and I cannot seem to create a 1:many relationship. I have also tried to replace the null values with the text 'Blank' to no avail.

I do not fully understanding how Power Bi treats null values. Does anyone know how to manage this?

Here is the screenshot of the relationship window that tells me I cannot have a 1:many relationship.