Connection.getFeeForMessage() type hints do not consider the null value

[PirosB3]

Problem

The getFeeForMessage() method on the Connection class can return both a number and null value, which is inconsistent with the types defined in the TypeScript package.

Steps to reproduce:

• Import and initialize the Connection object from the library
• Call getFeeForMessage() on a Connection instance, and pass an expired blockhash
• Observe that both a number and null value can be returned.

Expected outcome: The getFeeForMessage() function should only return a number, as indicated by the types defined in the TypeScript package, or throw an error.
Actual outcome: The function returns both a number and null value, causing unexpected behavior in the code.

Proposed Solution

2 Solutions come to my mind:

• raise an error if the RPC call returns null - no need to change the types
• change the return type from RpcResponseAndContext<number> to RpcResponseAndContext<number | null>