[arturobernalg]

Environment#getCommandLineOption always returned a non-null value for a VOID-type option (e.g. mvnd.serial) whenever any of its prefixes matched, regardless of what followed. -Dmvnd.serial=false and --serial=false were therefore indistinguishable from --serial, so an explicit "false" turned serial mode ON instead of leaving it off.

Inspect the text after the matched prefix and treat an explicit "false" (case-insensitive) as turning the option off.

Backport of the Environment.java part of #1855 from master, adapted to this branch: mvnd-1.x has since diverged (DefaultClient.java is split into java-mvnd/java-fallback source sets here, unlike master's single source set), so this backport is scoped to the independently reproducible and testable VOID-option bug. The other fixes bundled in #1855 (blank-argument handling, maven.config-aware threads/builder defaults, active-daemon log purge) touch the java-mvnd-only DefaultClient class, which this branch's test-compile classpath cannot resolve against (it resolves symbols against the java-fallback class instead), so they are left for a separate change.

Added EnvironmentTest#voidOptionHonoursExplicitFalse, which fails on the current code and passes with the fix. Full client+common suite: 15/15 tests green. Checkstyle: no new violations on the touched lines (the branch has pre-existing, unrelated violations elsewhere).

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