Replacing PUBLIC_EXPRESSION_REGEX.match(field) with parse_expression(field) is incorrect: parse_expression uses MRI_EXPRESSION_REGEX which requires MRI format (entity:namespace/name@unit), so public fields like sum(session.duration) never match, causing operation=None and metric_name="sum(session.duration)", which then fails inside get_mri() with InvalidParams("Failed to parse 'sum(session.duration)'") for every API call with a public metric field.