You can do this in two ways:
- In query-editor (follow the steps below)
1) In your power bi desktop, click on edit queries.
2) Select column right-clicks on it.
3) Choose to replace the value.
4) Enter "null" in find value in "replace value enter "0"
5) Close and apply
*You should see "0" wherever you have nulls in that column.
- Using the new calculated measure
Create a new measure using the following code :
Column = IF(ISBLANK(**original column**),0,**original column**)
**original column** - your name for the column you are using.
Then change the value to the new column and it should work.