liquibase-core/src/main/java/liquibase/util/CollectionUtil.java
public static <T> Set<T> createIfNull(Set<T> currentValue) {
        if (currentValue == null) {
            return new HashSet<>();
        } else {
            return currentValue;
        }
    }
public static <T> Set<T> createIfNull(Set<T> currentValue) {
        if (currentValue == null) {
            return new HashSet<>();
        } else {
            return currentValue;
        }
    }
Returns a new empty set if the passed array is null.