liquibase-core/src/main/java/liquibase/change/ChangeMetaData.java
public Map<String, ChangeParameterMetaData> getRequiredParameters(Database database) {
        Map<String, ChangeParameterMetaData> returnMap = new HashMap<>();

        for (ChangeParameterMetaData metaData : parameters.values()) {
            if (metaData.isRequiredFor(database)) {
                returnMap.put(metaData.getParameterName(), metaData);
            }
        }
        return returnMap;
    }
public Map<String, ChangeParameterMetaData> getRequiredParameters(Database database) {
        Map<String, ChangeParameterMetaData> returnMap = new HashMap<>();

        for (ChangeParameterMetaData metaData : parameters.values()) {
            if (metaData.isRequiredFor(database)) {
                returnMap.put(metaData.getParameterName(), metaData);
            }
        }
        return returnMap;
    }
Returns the required parameters for this change for the given database. Will never return a null map, only an empty or populated map.