fix: interpret missing point as zero value in formula evaluation (Sig…

…Noz#4668)

pkg/query-service/app/formula.go

@@ -87,23 +87,6 @@ func joinAndCalculate(results []*v3.Result, uniqueLabelSet map[string]string, ex
 		}
 	}
 
-	vars := expression.Vars()
-	var doesNotHaveAllVars bool
-	for _, v := range vars {
-		if _, ok := seriesMap[v]; !ok {
-			doesNotHaveAllVars = true
-			break
-		}
-	}
-
-	// There is no series that matches the label set from all queries
-	// TODO: Does the lack of a series from one query mean that the result should be nil?
-	// Or should we interpret the series as having a value of 0 at all timestamps?
-	// The current behaviour with ClickHouse is to show no data
-	if doesNotHaveAllVars {
-		return nil, nil
-	}
-
 	resultSeries := &v3.Series{
 		Labels: uniqueLabelSet,
 	}