6-9 - Duplicate Serial Number ID

Possible Causes

1. An empty object was returned.
2. A custom serial number class, org.apache.dubbo.common.serialize.Serialization#getContentTypeId, duplicates with the system built-in. In this case, the first loaded SPI instance will prevail. Other entries will be skipped.

Troubleshooting and Resolution Steps

1. Check the return result.
2. Built-in values can refer to the class org.apache.dubbo.common.serialize.Constants