liquibase-core/src/main/java/liquibase/util/StringClauses.java
public StringClauses append(String key, StringClauses subclauses) {
        Validate.notNull(StringUtil.trimToNull(key), "key must be a non-null, non-empty value");

        key = StringUtil.trimToEmpty(key).toLowerCase();

        if (clauses.containsKey(key)) {
            throw new IllegalArgumentException("Cannot add clause with key '" + key + "' because it is already defined");
        }

        clauses.put(key, subclauses);
        return this;
    }
public StringClauses append(String key, StringClauses subclauses) {
        Validate.notNull(StringUtil.trimToNull(key), "key must be a non-null, non-empty value");

        key = StringUtil.trimToEmpty(key).toLowerCase();

        if (clauses.containsKey(key)) {
            throw new IllegalArgumentException("Cannot add clause with key '" + key + "' because it is already defined");
        }

        clauses.put(key, subclauses);
        return this;
    }
Adds a new sub-clause at the end of the list with the given key.