function getExport(defaultExport) {
  return this._toExport || defaultExport
}
If the export was wrapped, that wrapper is returned, otherwise `defaultExport`.

@private
@memberof Shim.prototype
@param {*} defaultExport - The original export in case it was never wrapped.
@returns {*} The result from calling {@link Shim#wrapExport} or `defaultExport`
 if it was never used.
@see Shim.wrapExport