_checkStep(sStepName, aInputIds) {
			const oWizard = this.byId("shoppingCartWizard");
			const oStep = this.byId(sStepName);
			const bEmptyInputs = this._checkInputFields(aInputIds);
			const bValidationError = !!Messaging.getMessageModel().getData().length;

			if (!bValidationError && !bEmptyInputs) {
				oWizard.validateStep(oStep);
			} else {
				oWizard.invalidateStep(oStep);
			}
		}
Hides button to proceed to next WizardStep if validation conditions are not fulfilled.
@param {string} sStepName - the ID of the step to be checked
@param {array} aInputIds - Input IDs to be checked