test: Add missing test cases

src/compat/string/trim.spec.ts

@@ -27,6 +27,7 @@ describe('trim', () => {
     const expected = `a-b-c`;
 
     expect(func(string, '_-')).toBe(expected);
+    expect(func(string, ['_', '-'])).toBe(expected);
   });
 
   it(`\`trim\` should coerce \`chars\` to a string`, () => {

src/string/trim.ts

@@ -14,7 +14,7 @@ import { trimEnd } from './trimEnd.ts';
  * trim("##hello##", ["#", "o"]); // "hell"
  */
 export function trim(str: string, chars?: string | string[]): string {
-  if (chars == null) {
+  if (chars === undefined) {
     return str.trim();
   }
 

src/string/trimEnd.ts

@@ -12,7 +12,7 @@
  * const trimmedStr4 = trimEnd('trimmedxxx', 'x') // returns 'trimmed'
  */
 export function trimEnd(str: string, chars?: string | string[]): string {
-  if (chars == null) {
+  if (chars === undefined) {
     return str.trimEnd();
   }
 

src/string/trimStart.ts

@@ -12,7 +12,7 @@
  * const trimmedStr4 = trimStart('xxxtrimmed', 'x') // returns 'trimmed'
  */
 export function trimStart(str: string, chars?: string | string[]): string {
-  if (chars == null) {
+  if (chars === undefined) {
     return str.trimStart();
   }
   let startIndex = 0;