Custom Column and Names

I have Custom Column where I combine 4 columns of which 3 are Employee Names.

I use = [Employee Last Name]&", "&[Employee First Name]&" "&[Employee Middle Name]&" - "&[Employee Birth Date Text]

This works until there is no Employee Middle Name and it returns null values in the combined column.

How do I include values for Last. First and Birth Date Text if there is no middle name? .