Argument of type 'string | null' is not assignable to parameter of type 'string'. Type 'null' is not assignable to type 'string'. TS2345 code example

Example: Argument of type 'string | null' is not assignable to parameter of type 'string'. Type 'null' is not assignable to type 'string'

this.currentUser = JSON.parse(localStorage.getItem('currentUser') || '{}');