Section 4 - Rules of construction1. The rule that statutes in derogation of the common law are to be strictly construed shall have no application to this chapter.2. The law of estoppel shall apply under this chapter.3. The law of agency shall apply under this chapter.4. This chapter shall be so interpreted and construed as to effect its general purpose to make uniform the law of those states which enact it.5. This chapter shall not be construed so as to impair the obligations of any contract existing when the chapter goes into effect, nor to affect any action or proceedings begun or right accrued before this chapter takes effect.