MapToString.java

public static String mapToString(Map<String, String> map, String kvSeparator, String setSeparator) {
    StringBuilder stringBuilder = new StringBuilder();
    
    for (String key : map.keySet()) {
        if (stringBuilder.length() > 0) stringBuilder.append(setSeparator);
        String value = map.get(key);
        stringBuilder.append((key != null ? key : "null"));
        stringBuilder.append(kvSeparator);
        stringBuilder.append(value != null ? value : "null");
    }
    
    return stringBuilder.toString();
}