liquibase-core/src/main/java/liquibase/util/CollectionUtil.java
public static <T> List<T> createIfNull(List<T> currentValue) {
        if (currentValue == null) {
            return new ArrayList<T>();
        } else {
            return currentValue;
        }
    }
public static <T> List<T> createIfNull(List<T> currentValue) {
        if (currentValue == null) {
            return new ArrayList<T>();
        } else {
            return currentValue;
        }
    }
Returns passed currentValue if it is not null and creates a new ArrayList if it is null.
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Example: values = createIfNull(values)