feat: Make isEmpty a type guard (silvermine#16)

src/utils/is-empty.ts

@@ -4,6 +4,27 @@ import { isArguments } from './is-arguments';
 import { isUndefined } from './is-undefined';
 import { isSet } from './is-set';
 
+
+interface IEmptyArguments extends IArguments {
+   length: 0;
+}
+
+interface IEmptyObj {
+   [s: string]: never;
+}
+
+type IEmptyTypes = (
+   null |
+   undefined |
+   boolean |
+   number |
+   never[] |
+   '' |
+   IEmptyArguments |
+   Set<never> |
+   IEmptyObj
+);
+
 /**
  * Checks if `o` is an empty object. An object is "empty" if it:
  *
@@ -13,7 +34,7 @@ import { isSet } from './is-set';
  *
  * @returns `true` if `o` is empty
  */
-export function isEmpty(o: any): boolean {
+export function isEmpty(o: any): o is IEmptyTypes {
    if (o === null || isUndefined(o)) {
       return true;
    }