code: public static Map<String, Object> getSubsetStartingWith(
  			final ServiceReference<?> serviceReference, final String prefix) {
  		final Map<String, Object> subset = new HashMap<>();
  		for (String key : serviceReference.getPropertyKeys()) {
  			if (key != null && key.startsWith(prefix)
  					&& key.trim().length() > prefix.length()) {
  				subset.put(key.substring(prefix.length()),
  						serviceReference.getProperty(key));
  			}
  		}
  		if (subset.isEmpty()) {
  			return null;
  		}
  		return subset;
  	}
docs: Returns the subset of properties that start with the prefix. The returned
  dictionary will have as keys the original key without the prefix.
  
  @param serviceReference service reference; cannot be null
  @param prefix           property keys prefix; cannot be null
  @return subset of properties or null if there is no property that starts
  with expected prefix