params property Null safety

1. sendbird_sdk
2. user_message_send_request
3. ChannelUserMessageSendRequest
4. params property

ChannelUserMessageSendRequest class

1. Constructors
2. ChannelUserMessageSendRequest
3. Properties
4. channelType
5. channelUrl
6. cmd
7. encoded
8. hashCode
9. isAckRequired
10. params
11. payload
12. pending
13. requestId
14. runtimeType
15. Methods
16. noSuchMethod
17. toString
18. Operators
19. operator ==