n11 Under California law, even in the absence of a confidential or fiduciary relationship, a contract may be void if the person seeking relief proves undue influence. (See Civ. Code, § 1575.) In such circumstances, the plaintiff must prove that the defendant took unfair advantage of the plaintiff's weakness of mind or "grossly oppressive and unfair advantage of another's necessities or distress." (Ibid.) The court hearing such a claim will consider matters such as the substantial weakness of the person influenced or the excessive strength of the other party, taking into account factors such as the transaction having occurred at an unusual or inappropriate time or place, an insistent demand that the business be concluded immediately without recourse to independent advisers and an extreme emphasis on the negative consequences of delay, the concurrence of several persons in influencing the weaker party, and the absence of an independent adviser for that person.