code: static Field getClassFieldByName(Class<?> clazz, String fieldName) {
          try {
              return clazz.getDeclaredField(fieldName);
          } catch (SecurityException e) {
              throw new DynamoDBMappingException(
                      "Denied access to the [" + fieldName + "] field in class [" + clazz + "].", e);
          } catch (NoSuchFieldException e) {
              return null;
          }
      }
docs: Returns the Field object for the specified field name declared in the
  specified class. Returns null if no such field can be found.
  
  @param clazz
  The declaring class where the field will be reflected. This
  method will NOT attempt to reflect its superclass if such
  field is not found in this class.
  @param fieldName
  The case-sensitive name of the field to be searched.