fenzo-triggers/src/main/java/com/netflix/fenzo/triggers/persistence/AbstractInMemoryDao.java
protected String extractGroupFromId(String columnName) {
        if (columnName == null || !columnName.contains(idSeparator)) return columnName;
        String[] tokens = columnName.split(idSeparator);
        if (tokens.length == 2) {
            return tokens[0];
        } else {
            throw new IllegalArgumentException(String.format("Cannot extract row key from column name string: %s", columnName));
        }
    }
protected String extractGroupFromId(String columnName) {
        if (columnName == null || !columnName.contains(idSeparator)) return columnName;
        String[] tokens = columnName.split(idSeparator);
        if (tokens.length == 2) {
            return tokens[0];
        } else {
            throw new IllegalArgumentException(String.format("Cannot extract row key from column name string: %s", columnName));
        }
    }
@warn method description missing
@warn parameter columnName description missing
@warn exception IllegalArgumentException description missing

@param columnName
@return
@throws IllegalArgumentException