[BUG] the field "extMap" cant transmission after send

[pokid]

OpenIM Server Version

3.8

Operating System and CPU Architecture

Linux (AMD)

Deployment Method

Docker Deployment

Bug Description and Steps to Reproduce

1、set "extMap" value
2、send message and wait send success
3、get the message field "extMap",its size is 0

and i try "ext" field,"ext" filed is ok.

Screenshots Link

before send:

after send:

[FGadvancer]

Could you tell me specifically which platform's SDK it is, so that we can fix the issue more easily.

[pokid]

Could you tell me specifically which platform's SDK it is, so that we can fix the issue more easily.

hi,it flutter sdk