DevEncoded/bytearray commands flawed in Python 3

(using PyTango 9.3.0, Python 3.7.3)

In a test Tango server, I have the following command:

@command(dtype_in=bytearray)
def DevSerWriteChar(self, chars):
    self.buf += chars

When calling it from a PyTango client like this:

>>> dev_proxy.DevSerWriteChar(bytearray(b"HELLO"))

I get the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/matias/miniconda2/envs/bliss/lib/python3.7/site-packages/tango/device_proxy.py", line 243, in f
    return dp.command_inout(name, *args, **kwds)
  File "/home/matias/miniconda2/envs/bliss/lib/python3.7/site-packages/tango/green.py", line 195, in greener
    return executor.run(fn, args, kwargs, wait=wait, timeout=timeout)
  File "/home/matias/miniconda2/envs/bliss/lib/python3.7/site-packages/tango/green.py", line 109, in run
    return fn(*args, **kwargs)
  File "/home/matias/miniconda2/envs/bliss/lib/python3.7/site-packages/tango/connection.py", line 108, in __Connection__command_inout
    r = Connection.command_inout_raw(self, name, *args, **kwds)
  File "/home/matias/miniconda2/envs/bliss/lib/python3.7/site-packages/tango/connection.py", line 136, in __Connection__command_inout_raw
    param = __get_command_inout_param(self, cmd_name, cmd_param)
  File "/home/matias/miniconda2/envs/bliss/lib/python3.7/site-packages/tango/connection.py", line 57, in __get_command_inout_param
    param.insert(info.in_type, cmd_param)
TypeError: No registered converter was able to extract a C++ pointer to type char from this Python object of type int

As far as I have seen, bytearray is converted to DevEncoded - but it seems something is missing to handle it properly ? Or maybe I am doing something wrong ?