HttpTranslator constructor Null safety

1. spine_client
2. http_client
3. HttpTranslator
4. HttpTranslator constructor

HttpTranslator class

1. Constructors
2. HttpTranslator
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. body
8. headers
9. noSuchMethod
10. toString
11. translate
12. Operators
13. operator ==