Address issue 18662 to display accurate error messages. (#18663)

* Address issue 18662 to display accurate error messages.

* Update CHANGELOG.next.asciidoc

* Add common.MapStr to check and perform type assertion for subData.

CHANGELOG.next.asciidoc

@@ -101,6 +101,7 @@ field. You can revert this change by configuring tags for the module and omittin
 - Change `decode_json_fields` processor, to merge parsed json objects with existing objects in the event instead of fully replacing them. {pull}17958[17958]
 - [Autodiscover] Check if runner is already running before starting again. {pull}18564[18564]
 - Fix `keystore add` hanging under Windows. {issue}18649[18649] {pull}18654[18654]
+- Fix an issue where error messages are not accurate in mapstriface. {issue}18662[18662] {pull}18663[18663]
 
 *Auditbeat*
 

libbeat/common/schema/mapstriface/mapstriface.go

@@ -98,23 +98,23 @@ func (convMap ConvMap) Map(key string, event common.MapStr, data map[string]inte
 		err.Required = convMap.Required
 		return multierror.Errors{err}
 	}
-	subData, ok := d.(map[string]interface{})
-	if !ok {
+	switch subData := d.(type) {
+	case map[string]interface{}, common.MapStr:
+		subEvent := common.MapStr{}
+		_, errors := convMap.Schema.ApplyTo(subEvent, subData.(map[string]interface{}))
+		for _, err := range errors {
+			if err, ok := err.(schema.KeyError); ok {
+				err.SetKey(convMap.Key + "." + err.Key())
+			}
+		}
+		event[key] = subEvent
+		return errors
+	default:
 		msg := fmt.Sprintf("expected dictionary, found %T", subData)
 		err := schema.NewWrongFormatError(convMap.Key, msg)
 		logp.Err(err.Error())
 		return multierror.Errors{err}
 	}
-
-	subEvent := common.MapStr{}
-	_, errors := convMap.Schema.ApplyTo(subEvent, subData)
-	for _, err := range errors {
-		if err, ok := err.(schema.KeyError); ok {
-			err.SetKey(convMap.Key + "." + err.Key())
-		}
-	}
-	event[key] = subEvent
-	return errors
 }
 
 func (convMap ConvMap) HasKey(key string) bool {