// Just returning an Integer with the index here is faster, but requires a lot of if/then/else to check for
            // -1
            //  or QUALIFIERS.size and then resort to lexical ordering. Most comparisons are decided by the first
            // character,
            // so this is still fast. If more characters are needed then it requires a lexical sort anyway.

                .flatMap(Function.identity())
                .collect(toSet());
    }

    /**
     * Check whether the required profiles were found in any of the projects we're building or the settings.
     * @param session the Maven session.
     * @param profileActivation the requested optional and required profiles.
     */
    private void validateRequiredProfiles(MavenSession session, ProfileActivation profileActivation) {

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