NERtcEncryptionMode constructor Null safety

1. nertc
2. nertc
3. NERtcEncryptionMode
4. NERtcEncryptionMode const constructor

NERtcEncryptionMode enum

1. Constructors
2. NERtcEncryptionMode
3. Values
4. GMCryptoSM4ECB
5. Properties
6. hashCode
7. index
8. runtimeType
9. Methods
10. noSuchMethod
11. toString
12. Operators
13. operator ==
14. Constants
15. values