new_contents: import pytest
  from plenum.common.messages.fields import SerializedValueField
  
  validator = SerializedValueField()
  
  
  def test_non_empty_string():
      assert not validator.validate("x")
  
  
  def test_empty_string():
      assert validator.validate("")
  
  
  def test_non_empty_bytes():
      assert not validator.validate(b"hello")
  
  
  def test_empty_bytes():
      assert validator.validate(b"")
  
subject: add test for SerializedValueField