single pad sink hier block fails but similar two output block works

Version: 3.10.11.0-1

I have a simple hier block with two output pad sinks that works as
expected. These two outputs are nearly identical but independent
streams. I created a very similar hier block with only a single stream
and one output pad sink.  Executing a flow graph containing the latter
hier block generates the error:

".local/lib64/python3.11/site-packages/gnuradio/gr/hier_block2.py", line
126, in connect
    self.primitive_connect(*args)
ValueError: port number 0 exceeds max of (none)

The offending line 126:

    def connect(self, *args):
        """
        Connect two or more block endpoints.  An endpoint is either a
(block, port)
        tuple or a block instance.  In the latter case, the port number
is assumed
        to be zero.

        To connect the hierarchical block external inputs or outputs to
internal block
        inputs or outputs, use 'self' in the connect call.

        If multiple arguments are provided, connect will attempt to
wire them in series,
        interpreting the endpoints as inputs or outputs as appropriate.
        """
        self.primitive_connect(*args)


Working two output block init:

    def __init__(self, E6bCode_file='0', E6cCode_file='0'):
        gr.hier_block2.__init__(
            self, "E6bc_code_source",
                gr.io_signature(0, 0, 0),
                gr.io_signature.makev(2, 2, [gr.sizeof_float*1,
gr.sizeof_float*1]),
        )


errant single output block init:

    def __init__(self, HxCode_file='0'):
        gr.hier_block2.__init__(
            self, "Hx_code_source",
                gr.io_signature(0, 0, 0),
                gr.io_signature(1, 1, gr.sizeof_float*1),
        )


Is there a place I should look for the root of the problem? I am
struggling to understand this. I thought to ask now in anticipation of
still struggling at the end of the day.


Rick