InsertOpts() Metadata

It seems that Metadata is ignored when provided as a part JobArgsWithInsertOpts.InsertOpts().
When specified as a part of third param to Client.Insert they are applied just fine.

The problem I see is that insertParamsFromArgsAndOptions neglects JobArgsWithInsertOpts meta and always takes what was passed as a function arg. Actually I do agree that the function arg should have higher priority and override what was specified in JobArgsWithInsertOpts.InsertOpts(), but when the arg is empty I'd expect job's meta to take effect.

Important pieces below:

if insertOpts == nil {
	insertOpts = &InsertOpts{}
}

var jobInsertOpts InsertOpts
if argsWithOpts, ok := args.(JobArgsWithInsertOpts); ok {
	jobInsertOpts = argsWithOpts.InsertOpts()
}

metadata := insertOpts.Metadata
if len(metadata) == 0 {
	metadata = []byte("{}")
}