Returns 'null' from resolve id hook rather than undefined to fix compatibility issue with newest Rollup version

Author: wessberg

package.json

@@ -52,7 +52,7 @@
 "@wessberg/scaffold": "^1.0.18",
 "@wessberg/ts-config": "^0.0.41",
 "standard-changelog": "^2.0.11",
-"@wessberg/rollup-plugin-ts": "^1.1.56",
+"@wessberg/rollup-plugin-ts": "^1.1.57",
 "tslint": "^5.17.0",
 "prettier": "^1.18.2",
 "pretty-quick": "^1.11.1",

src/plugin/typescript-plugin.ts

@@ -345,11 +345,11 @@ export default function typescriptRollupPlugin(pluginInputOptions: Partial<Types
  * Attempts to resolve the given id via the LanguageServiceHost
  * @param {string} id
  * @param {string} parent
- * @returns {string | void}
+ * @returns {string | null}
  */
-resolveId(this: PluginContext, id: string, parent: string | undefined): string | undefined {
+resolveId(this: PluginContext, id: string, parent: string | undefined): string | null {
 // Don't proceed if there is no parent (in which case this is an entry module)
-if (parent == null) return undefined;
+if (parent == null) return null;
 
 return resolveId({id, parent, cwd, options: parsedCommandLineResult.parsedCommandLine.options, moduleResolutionHost, resolveCache});
 },

src/util/resolve-id/resolve-id.ts

@@ -4,15 +4,14 @@ import {isBuiltInModule} from "../module/module-util";
 /**
  * Resolves an id from the given parent
  * @param {IResolveModuleOptions} opts
- * @returns {string?}
+ * @returns {string|null}
  */
-export function resolveId({id, parent, options, cwd, moduleResolutionHost, resolveCache}: IResolveModuleOptions): string | undefined {
+export function resolveId({id, parent, options, cwd, moduleResolutionHost, resolveCache}: IResolveModuleOptions): string | null {
 // Don't proceed if there is no parent (in which case this is an entry module)
-if (parent == null) return undefined;
+if (parent == null) return null;
 
 // Don't attempt to load built-in modules
-if (isBuiltInModule(id)) return undefined;
+if (isBuiltInModule(id)) return null;
 
-const resolveMatch = resolveCache.get({id, parent, cwd, options, moduleResolutionHost});
-return resolveMatch == null ? undefined : resolveMatch;
+return resolveCache.get({id, parent, cwd, options, moduleResolutionHost});
 }