List - Filling In Each Blank Cells With Value Contained In First Non-blank Cell Above It

I have a list that looks something like this:

Column B

Row 4 Item 1
Row 5 Item 2
Row 6
Row 7
Row 8 Item 3
Row 9
Row 10 Item 4
Row 11
Row 12
Row 13
Row 14 Item 5

The range of cells in column B containing the items has a name "ColStreams"

I need to go through the list, filling in each blank cells with the value contained in the first non-blank cell above it - so, in this case, rows 6 and 7 would contain "Item 2", row 9 would contain "Item 3", rows 11-13 would contain "Item 4" and so on.