If the `buildContainerImage` method is called without passing any
arguments at all, the `args` object will be `null`. Attempting to
access the properties of it in that case raises a
`NullPointerException`. Fortunately, Groovy has a `?` operator that
returns `null` when the named object is `null` and avoids accessing its
properties.
The `buildContainerImage` method now supports an optional `arch` keyword
argument. This argument can be used to select the architecture of the
node running the pod building the container image. If unspecified, it
defaults to `amd64`.
The `registry`, `project`, `name`, and `tag` values can now be passed as
keyword arguments to the `buildContainerImage` function. This will
allow jobs to override the default values if necessary.
Dustin