liquibase-core/src/main/java/liquibase/util/StringClauses.java
public StringClauses getSubclause(String exitingKey) {
        exitingKey = StringUtil.trimToEmpty(exitingKey).toLowerCase();
        Object clauses = getImpl(exitingKey);
        if (clauses == null) {
            return null;
        }
        if (clauses instanceof String) {
            return new StringClauses().append((String) clauses);
        }
        return (StringClauses) clauses;
    }
public StringClauses getSubclause(String exitingKey) {
        exitingKey = StringUtil.trimToEmpty(exitingKey).toLowerCase();
        Object clauses = getImpl(exitingKey);
        if (clauses == null) {
            return null;
        }
        if (clauses instanceof String) {
            return new StringClauses().append((String) clauses);
        }
        return (StringClauses) clauses;
    }
Retrieves the given key. Returns null if not set. If clause at key is a String, return a new StringClause version of it. Will traverse sub-clauses to find the key.