fix: resolve jolokia2 panic on null response (#11397)

plugins/inputs/jolokia2/common/gatherer.go

@@ -94,7 +94,13 @@ func (g *Gatherer) generatePoints(metric Metric, responses []ReadResponse) ([]po
 		}
 
 		pb := NewPointBuilder(metric, response.RequestAttributes, response.RequestPath)
-		for _, point := range pb.Build(metric.Mbean, response.Value) {
+		ps, err := pb.Build(metric.Mbean, response.Value)
+		if err != nil {
+			errors = append(errors, err)
+			continue
+		}
+
+		for _, point := range ps {
 			if response.RequestTarget != "" {
 				point.Tags["jolokia_agent_url"] = response.RequestTarget
 			}

plugins/inputs/jolokia2/common/point_builder.go

@@ -27,15 +27,15 @@ func NewPointBuilder(metric Metric, attributes []string, path string) *pointBuil
 }
 
 // Build generates a point for a given mbean name/pattern and value object.
-func (pb *pointBuilder) Build(mbean string, value interface{}) []point {
+func (pb *pointBuilder) Build(mbean string, value interface{}) ([]point, error) {
 	hasPattern := strings.Contains(mbean, "*")
-	if !hasPattern {
+	if !hasPattern || value == nil {
 		value = map[string]interface{}{mbean: value}
 	}
 
 	valueMap, ok := value.(map[string]interface{})
-	if !ok { // FIXME: log it and move on.
-		panic(fmt.Sprintf("There should be a map here for %s!\n", mbean))
+	if !ok {
+		return nil, fmt.Errorf("the response of %s's value should be a map", mbean)
 	}
 
 	points := make([]point, 0)
@@ -46,7 +46,7 @@ func (pb *pointBuilder) Build(mbean string, value interface{}) []point {
 		})
 	}
 
-	return compactPoints(points)
+	return compactPoints(points), nil
 }
 
 // extractTags generates the map of tags for a given mbean name/pattern.