Returning value types rather than pointers

[peteski22]

Why are you returning an empty ServerEntry struct instead of nil?

Originally posted by @dpoulopoulos in #173

There are places in the existing code base where we should consider returning a value type over a pointer...

e.g. DefaultCacheTTL and transformValueArg

But also, some places that should likely stay as they are, returning a pointer:

• NewHealthTracker
• NewClientManager
• NewExecutionContextConfig
• NewCLIArgParser

Because they manage a lot of state or deal with large structs.

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Refactor the following to return value types not pointers:

• DefaultCacheTTL
• transformValueArg