protected void start() {
            if (start == null) {
                start = MonotonicClock.now();
                resumed = start;
            } else {
                resumed = MonotonicClock.now();
            }
        }

        protected void stop() {
            end = MonotonicClock.now();
            exec = exec.plus(Duration.between(resumed, end));
        }

        }
    }

    /**
     * Returns new builder from scratch.
     */
    static Builder newBuilder() {
        return new Builder().withStartTime(MonotonicClock.now());
    }

    class Builder {
        private Map<String, String> userProperties;
        private Map<String, String> systemProperties;
        private Instant startTime;

import java.util.regex.Pattern;
import java.util.stream.Collectors;

import org.apache.maven.InternalErrorException;
import org.apache.maven.Maven;
import org.apache.maven.api.Constants;
import org.apache.maven.api.MonotonicClock;
import org.apache.maven.api.annotations.Nullable;
import org.apache.maven.api.cli.InvokerRequest;
import org.apache.maven.api.cli.Logger;
import org.apache.maven.api.cli.mvn.MavenOptions;