Make JSON format compatible with nulls (#9110)

plugins/parsers/json/parser.go

@@ -193,10 +193,13 @@ func (p *Parser) Parse(buf []byte) ([]telegraf.Metric, error) {
 	if p.query != "" {
 		result := gjson.GetBytes(buf, p.query)
 		buf = []byte(result.Raw)
-		if !result.IsArray() && !result.IsObject() {
-			err := fmt.Errorf("E! Query path must lead to a JSON object or array of objects, but lead to: %v", result.Type)
+		if !result.IsArray() && !result.IsObject() && result.Type != gjson.Null {
+			err := fmt.Errorf("E! Query path must lead to a JSON object, array of objects or null, but lead to: %v", result.Type)
 			return nil, err
 		}
+		if result.Type == gjson.Null {
+			return nil, nil
+		}
 	}
 
 	buf = bytes.TrimSpace(buf)
@@ -217,6 +220,8 @@ func (p *Parser) Parse(buf []byte) ([]telegraf.Metric, error) {
 		return p.parseObject(v, timestamp)
 	case []interface{}:
 		return p.parseArray(v, timestamp)
+	case nil:
+		return nil, nil
 	default:
 		return nil, ErrWrongType
 	}

plugins/parsers/json/parser_test.go

@@ -892,6 +892,18 @@ func TestParse(t *testing.T) {
 			input:    []byte(`[]`),
 			expected: []telegraf.Metric{},
 		},
+		{
+			name:     "parse null",
+			config:   &Config{},
+			input:    []byte(`null`),
+			expected: []telegraf.Metric{},
+		},
+		{
+			name:     "parse null with query",
+			config:   &Config{Query: "result.data"},
+			input:    []byte(`{"error":null,"result":{"data":null,"items_per_page":10,"total_items":0,"total_pages":0}}`),
+			expected: []telegraf.Metric{},
+		},
 		{
 			name: "parse simple array",
 			config: &Config{