Today I learned about the subtleties of build arguments in Dockerfile definitions, specifically how the ARG instruction relates to - and is affected by - the FROM instruction. It's not entirely like a constant or a variable, in the way that I had thought.The problem with empty ARG valuesI spent more than a coffee's worth of time trying to understand why my custom builds of a CAP Node.js container image weren't of the CAP version I was specifying, either implicitly with the default value I'd decl...