code: public Object extractFieldValue(final Object instance, final Field field) {
      JBBPUtils.assertNotNull(field, "Field must not be null");
      try {
        return ReflectUtils.makeAccessible(field).get(instance);
      } catch (Exception ex) {
        throw new JBBPException("Can't extract value from field for exception", ex);
      }
    }
docs: Auxiliary method to extract field value.
  
  @param instance object instance, can be null
  @param field    the filed which value should be extracted, must not be null
  @return the field value