bugfix: query parameters and headers don't work properly with unknown values

[ms-henglu]

fixes #711

[magodo]

Shall we state this is a limitation, instead of silently ignore them and return empty query/header? Ideally, I think we shall split the header/query between different operations, e.g. read_header, create_header, etc.

[ms-henglu]

Shall we state this is a limitation, instead of silently ignore them and return empty query/header? Ideally, I think we shall split the header/query between different operations, e.g. read_header, create_header, etc.

We only convert the headers/query parameters from types.Map to go type in the CRUD functions, these values must be known at that time.