null check doesn't safeguard against non-existing values in the BOM config

BIGTOP-2051 has switched the build to use configuration properties instead of java properties. One of the unfortunate side effects of such dynamism is that null checks don't work as expected anymore, as empty elements of the config would be assigned with a ConfigObject instance even after simply null check. That leads to failures for component builds where some elements are omitted all-together, e.g bigtop-utils.

Instead of null checks I propose to user .isEmpty()