fix a TS issue

src/Complex/type.ts

@@ -7,7 +7,7 @@ export type Complex<T> = { re: T; im: T; }
 export const Complex_type = {
    test: <T>(dep: { testT: (z: unknown) => z is T }) =>
       (z: unknown): z is Complex<T> =>
-         typeof z === 'object' && 're' in z && 'im' in z
+         typeof z === 'object' && z != null && 're' in z && 'im' in z
          && dep.testT(z.re) && dep.testT(z.im),
    infer: (dep: typeOfDependency) =>
       (z: Complex<unknown>) => joinTypes(dep.typeOf(z.re), dep.typeOf(z.im)),