Detailed steps to reproduce the problem?

While this isn't exactly a bug, it does lead to unexpected behavior. MergeClientOptions should always return a non-nil object.

Definition of done: what must be done to consider the task complete?

MergeClientOptions should always return a non-nil object.

The exact Go version used, with patch level:

go version go1.23.1 darwin/arm64

The exact version of the Go driver used:

2.0.0

Describe how MongoDB is set up. Local vs Hosted, version, topology, load balanced, etc.

NA

The operating system and version (e.g. Windows 7, OSX 10.8, ...)

macOS 15.0 (24A335)

Security Vulnerabilities

NA