liquibase-core/src/main/java/liquibase/configuration/LiquibaseConfiguration.java
public static synchronized LiquibaseConfiguration getInstance() {
        if (instance == null) {
            instance = new LiquibaseConfiguration();
            instance.init(new SystemPropertyProvider());
        }

        return instance;
    }
public static synchronized LiquibaseConfiguration getInstance() {
        if (instance == null) {
            instance = new LiquibaseConfiguration();
            instance.init(new SystemPropertyProvider());
        }

        return instance;
    }
Returns the singleton instance, creating it if necessary. On creation, the configuration is initialized with {@link liquibase.configuration.SystemPropertyProvider}