Fix types bug

Author: gitKrystan

transforms/ember-object/test.ts

@@ -125,10 +125,7 @@ function runTest(
   }
 }
 
-function runTransform(
-  input: string,
-  testPath: string
-): string | null | undefined {
+function runTransform(input: string, testPath: string): string {
   return applyTransform(
     transform,
     // NOTE: This version of options unused in the transform

types/jscodeshift/dist/testUtils.d.ts

@@ -6,5 +6,5 @@ declare module 'jscodeshift/dist/testUtils' {
     transformOptions: Options,
     fileInfo: FileInfo,
     testOptions?: { parser: Parser }
-  ): string | null | undefined;
+  ): string;
 }