Mock contract MockRebornMinter.sol causes Slither/Echidna failure

When running Echidna, it first runs slither the following way:
slither . --ignore-compile --print echidna --json -
See this line of code in Echidna.

That generates an error:

{"success": false, "error": "Traceback (most recent call last):\n  File \"/Users/tom/.pyenv/versions/3.7.7/lib/python3.7/site-packages/slither/__main__.py\", line 712, in main_impl\n    ) = process_all(filename, args, detector_classes, printer_classes)\n  File \"/Users/tom/.pyenv/versions/3.7.7/lib/python3.7/site-packages/slither/__main__.py\", line 82, in process_all\n    ) = process_single(compilation, args, detector_classes, printer_classes)\n  File \"/Users/tom/.pyenv/versions/3.7.7/lib/python3.7/site-packages/slither/__main__.py\", line 67, in process_single\n    return _process(slither, detector_classes, printer_classes)\n  File \"/Users/tom/.pyenv/versions/3.7.7/lib/python3.7/site-packages/slither/__main__.py\", line 114, in _process\n    printer_results = slither.run_printers()\n  File \"/Users/tom/.pyenv/versions/3.7.7/lib/python3.7/site-packages/slither/slither.py\", line 192, in run_printers\n    return [p.output(self._crytic_compile.target).data for p in self._printers]\n  File \"/Users/tom/.pyenv/versions/3.7.7/lib/python3.7/site-packages/slither/slither.py\", line 192, in <listcomp>\n    return [p.output(self._crytic_compile.target).data for p in self._printers]\n  File \"/Users/tom/.pyenv/versions/3.7.7/lib/python3.7/site-packages/slither/printers/guidance/echidna.py\", line 376, in output\n    call_parameters = _call_a_parameter(self.slither)\n  File \"/Users/tom/.pyenv/versions/3.7.7/lib/python3.7/site-packages/slither/printers/guidance/echidna.py\", line 318, in _call_a_parameter\n    \"signature\": _get_name(ir.function),\n  File \"/Users/tom/.pyenv/versions/3.7.7/lib/python3.7/site-packages/slither/printers/guidance/echidna.py\", line 37, in _get_name\n    if f.is_fallback or f.is_receive:\nAttributeError: 'StateVariable' object has no attribute 'is_fallback'\n", "results": {}}

This is caused by the MockRebornMinter.sol

A workaround is to delete that contract when running Echidna, but it would be good to figure out a better solution.

Start with MockRebornMinter.sol and reproduce the failure using slither . --ignore-compile --print echidna --json - while running Echidna. Read the reported Slither Echidna printer path and determine a project-side fix for the StateVariable/is_fallback error. Done means Echidna can run without deleting MockRebornMinter.sol or triggering this Slither failure.