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