The fact finder may proceed in the absence of any party that, after due notice, fails to be present or fails to obtain an adjournment. Fact finders shall treat any subject on which one party has taken a position that it is not a mandatory subject for bargaining in accordance with this rule. Findings of fact and recommendations may not be made solely on the default of a party, and the fact finder may require the participating party to submit evidence as may be required for making of the findings of fact and recommendations.