code: protected static void registerSensitiveKeys(Class<? extends JsonPayload> cls) {
  		List<Field> fields = RuntimeUtils.listFields(cls, new RuntimeUtils.FieldFilter() {
  			@Override
  			public boolean accept(Field field) {
  				return Modifier.isStatic(field.getModifiers()) && // static fields
  						field.getAnnotation(SensitiveDataKey.class) != null &&  // marked as 'sensitive'
  						field.getType().equals(String.class); // with type of String
  			}
  		});
  
  		if (fields.size() > 0) {
  			List<String> keys = new ArrayList<>(fields.size());
  			try {
  				for (Field field : fields) {
  					field.setAccessible(true);
  					String value = (String) field.get(null);
  					keys.add(value);
  				}
  				SENSITIVE_KEYS_LOOKUP.put(cls, keys);
  			} catch (Exception e) {
  				ApptentiveLog.e(e, "Exception while registering sensitive keys");
  				logException(e);
  			}
  		}
  	}
docs: region Sensitive Keys