My PowerQuery Returns NaN for Aggregate Function?

Powerquery supports a number of aggregation functions such as "sum", "avg", and "max" etc. Those aggregate functions are commonly used to compute numeric values of specific fields. However, if the fields contain mixtures of numeric and non-numeric values, the aggregate function wouldn't be able to compute and return a valid result. Instead, you may see "NaN" in the column.

Here is a quick example to get the sum of the field "byteSent" in the last 4 days. 

As you can see that the bytesSent returns "NaN" for all the days except 4/21 despite that the values are available for all 4 days.

The issue here is that there are numerous events with non-numeric values for the field bytesSent. The workaround is to add "bytesSent >= 0" to guarantee that all events returned from the initial filter are all numbers.