(a) No policy or contract of insurance shall be issued unless it contains the agreement of the insurer or insurers that it or they will promptly pay all benefits conferred by this chapter and all installments of the compensation that may be awarded or agreed upon to the person entitled to them and that the obligation shall not be affected by any default of the insured after the injury or by any default in giving notice required by such policy or otherwise. Such agreement shall be construed to be a direct promise by the insurer or insurers to the person entitled to compensation and shall be enforceable in his name.

(b) A policy of insurance issued under this chapter shall always first be construed as an agreement to pay compensation; and an insurer who issues a policy of compensation insurance to an employer not subject to this chapter shall not plead as a defense that the employer is not subject to the chapter; and an insurer who issues to an employer subject to this chapter a policy of compensation insurance covering an employee or employees ordinarily exempt from its provisions shall not plead the exemption as a defense. In either case compensation shall be paid to an injured employee or to the dependents of a deceased employee for a compensable accident as if the employer or the employee or both were subject to this chapter, the policy of compensation insurance constituting a definite contract between all parties concerned.