FIRSTNONBLANK Returns the first value in the column, column, filtered by the current context, where the expression is not blank.
Syntax
FIRSTNONBLANK(column,expression)
Parameters
Column – A column expression.
Expression – An expression evaluated for blanks for each value of column.
Return Value
A table containing a single column and single row with the computed first value.
Reference Data
https://docs.microsoft.com/en-us/dax/dax-function-reference