It happens because of the line:
new_ctx['$'] = yaql_utils.convert_input_data(data_context)
in the module mistral/utils/expression_utils.py
(Currently can be seen at https://github.com/openstack/mistral/blob/master/mistral/utils/expression_utils.py#L51)
The patch where this issue was introduced: https://review.openstack.org/#/c/477816/
It happens because of the line:
new_ctx['$'] = yaql_utils. convert_ input_data( data_context)
in the module mistral/ utils/expressio n_utils. py
(Currently can be seen at https:/ /github. com/openstack/ mistral/ blob/master/ mistral/ utils/expressio n_utils. py#L51)
The patch where this issue was introduced: https:/ /review. openstack. org/#/c/ 477816/