Join attributes by value in QGIS 3.4.3 Processing Modeler

I want to add only a few specific columns from the join table but there is no drop down list. When selecting manually I'm able to select only 1 column when trying more than 1 I'm not getting the desired results.

I have tried writing like

1] column1, column2

2] 'column1', 'column2'

3] "column1", "column2"

4] (column1), (column2)

5] (column1, column2)

But none of them works. Please help how I can add only few selected columns

PS: the drop down option is available in join attributes by field tool when I try to use it without the processing modeler

Answer

Separate field names with a colon, eg:

column1;column2

https://issues.qgis.org/issues/20005