I have the calculated parameter defined as the sum of two other keys, received on SNMP from different nodes.

While both nodes are accessible, the sum is considered correctly. As soon as one of nodes becomes inaccessible, value of the sum to be calculated stops, on the graph there is a rupture.

I believe, the reason that value of an element-composed in this expression, at impossibility it to receive, is defined as "undefined". And, accordingly, value of the calculated parameter (sum) in this case becomes undefined.

Whether it is possible, at use of keys in calculated elements of the data, at impossibility of their reception, their value to define as 0, instead of how "undefined"?