fix: validate unsupported fileExt mime types

src/modules/system/index.ts

@@ -1,3 +1,4 @@
+import { FakerError } from '../../errors/faker-error';
 import { ModuleBase } from '../../internal/module-base';
 
 const commonFileTypes = ['video', 'audio', 'image', 'text', 'application'];
@@ -175,7 +176,12 @@ export class SystemModule extends ModuleBase {
     const mimeTypes = this.faker.definitions.system.mime_type;
 
     if (typeof mimeType === 'string') {
-      return this.faker.helpers.arrayElement(mimeTypes[mimeType].extensions);
+      const entry = mimeTypes[mimeType];
+      if (entry == null) {
+        throw new FakerError(`MIME type ${mimeType} is not supported.`);
+      }
+
+      return this.faker.helpers.arrayElement(entry.extensions);
     }
 
     const extensionSet = new Set(

test/modules/system.spec.ts

@@ -1,6 +1,6 @@
 import { isMimeType, isSemVer } from 'validator';
 import { describe, expect, it } from 'vitest';
-import { faker } from '../../src';
+import { FakerError, faker } from '../../src';
 import { seededTests } from '../support/seeded-runs';
 import { times } from './../support/times';
 
@@ -190,6 +190,12 @@ describe('system', () => {
             )}]. Got "${actual}".`
           ).include(actual);
         });
+
+        it('should throw for unsupported mimeType', () => {
+          expect(() => faker.system.fileExt('application/not-real')).toThrow(
+            new FakerError('MIME type application/not-real is not supported.')
+          );
+        });
       });
 
       describe('fileName()', () => {