Polymer reset parameters format not working

问题

I am new to Polymer 2.0. I need to update a field called Print Name to set the values I put in First Name + Last Name. Currently I get a version of it that is not working as I get bad request. 'System.FormatException: Input string was not in a correct format.'

_updateField(e) {
                e.preventDefault();
                this.set('_contract.signeeContact.printName', [this._contract.signeeContact.firstName, this._contract.signeeContact.lastName]);
                // printName: ["firstName", "LastName"] // this is not correct it should be
                // printName: ["firstName LastName"] // correct request should look like this
            }

the format is not correct. Can someone give me a hand with this? Thank you in advance.

来源：https://stackoverflow.com/questions/65254872/polymer-reset-parameters-format-not-working