Don't consider null as an object (#55)

Author: komachi

src/utils/utils.ts

@@ -44,7 +44,7 @@ export function isString (value: any): value is string {
 
 export function isObject (value: any): boolean {
 
-  return typeof value === 'object';
+  return value !== null && typeof value === 'object';
 }
 
 export function isArray (value: any): boolean {
@@ -338,4 +338,4 @@ export function takeUntil (input: any[], predicate: CollectionPredicate) {
 
 export function takeWhile (input: any[], predicate: CollectionPredicate) {
   return takeUntil(input, (item: any, index: number, collection: any[]) => !predicate(item, index, collection));
-}
+}