Using DATEDIFF with "N/A" or Null in Dataset

[mumair]

So I am familiar with the datediff command, but I have some cells in my time columns that are N/A because we did not measure those times. I am trying to use the datediff command to calculate the difference in times between two columns, but I can't do so because not all of the cells in the column have a time in them. How do I get around this?

[mumair]

Update:

Here is my DAX code:

Column = IF('Time Log'[Start Time] = "N/A", "N/A", DATEDIFF('Time Log'[Start Time],'Time Log'[End Time], minute))

I am getting the following error: Expressions that yield variant data-type cannot be used to define calculated columns.

How do I fix this?

[KHorseman]

"N/A" is text and DATEDIFF returns a number. You need the two return values to agree in type. I would just return null for N/A

Column = IF('Time Log'[Start Time] = "N/A", BLANK(), DATEDIFF('Time Log'[Start Time],'Time Log'[End Time], minute))