A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
One of the possible way is to take help of a dummy helper column.
Assume that you have column-Z (which is right now blank and not used in your data).
In this column-Z put a formula such that wherever you have yr data in column-C, you put a word say "Data" or "SortThis" and wherever you have a blank in column-C you put a "" in column-Z.
Now modify the code to sort your data on Column-Z in Descending order as key1 and Column-C in Ascending order as key2.
This will bring all the blank cells to the bottom.
At the end you can delete the column-Z.
Hope this Helps.