Fix nil pointer dereference on Placement

[Jarema]

The check for empty object exposed a lack of check for *Placement before accessing its fields. This commit properly fixes it.

Signed-off-by: Tomasz Pietrek tomasz@nats.io

[wallyqs]

think we need coverage of sending empty objects on the other endpoints that might have been relying on filtering out empty fields.

also for this one need a test of sending unitialized placement like {“placement”: null}

[Jarema]

Will add a test. Did a brief check of others usages and it seems fine, but will test to be sure.

[Jarema]

Added a test, but I wonder if it makes sense to have it - empty object test achieves the same as JSApiLeaderStepdownRequest{Placement: nil}.

[Jarema]

Checked other endpoints that are using new function. We do not have pointers in them.

[wallyqs]

@Jarema you're right in this case placement has omitempty so result would be the same