Neb. Rev. Stat. § 14-532

A city of the metropolitan class may, when not required for any of the purposes specified in section 14-530 , temporarily invest funds contained in the special assessment sinking fund in securities of the United States Government, the State of Nebraska, the city, the county containing such city, or any publicly owned and operated municipal utilities of such city. All such investments shall be made so as to be closed out and realized upon whenever the proceeds so invested are needed for the purpose specified in such section. The proceeds of the special assessment sinking fund, insofar as required, may be used to complete the work under a contract where the contractor fails or refuses to perform such work.