LOOKUP TABLE -blank cell in the table array to return a figure

My lookup table works perfect until there is a blank cell. I need there to be a blank cell in the table array and I want the blank cell to return the figure in the col_index_num but it is just returning a blank value rather than the dollar amount. I have attached an example, if someone can help that would be great. I'm referring to the formula in cell C7, when C5 has nothing in it should lookup A21 and give the figure of 30