MavenBuildSpec discards the JDK version read from the JAR when no language version is recorded #1464

MavenBuildSpec.resolve_fields selects the JDK version with

selected_jdk_version = jdk_from_jar or existing if existing else "8"

Python parses this as (jdk_from_jar or existing) if existing else "8", so whenever the database has no recorded language_version, the JDK version just read from the Maven Central JAR is discarded and the build spec says Java 8, whatever the JAR was built with. The comment above the line describes the intended order, JAR first, then the existing value, then the default.

Reproduces on main at 16c6a1e: with language_version=[] and a JAR reporting 17, resolve_fields leaves language_version == ["8"]. A one-line fix with a parametrized test follows as a PR.