fix: null is invalid for sources and file (#242)

Author: bmeurer

src/Bundle.js

@@ -144,7 +144,7 @@ export default class Bundle {
 		});
 
 		return {
-			file: options.file ? options.file.split(/[/\\]/).pop() : null,
+			file: options.file ? options.file.split(/[/\\]/).pop() : undefined,
 			sources: this.uniqueSources.map((source) => {
 				return options.file ? getRelativePath(options.file, source.filename) : source.filename;
 			}),

src/MagicString.js

@@ -163,9 +163,9 @@ export default class MagicString {
 		});
 
 		return {
-			file: options.file ? options.file.split(/[/\\]/).pop() : null,
-			sources: [options.source ? getRelativePath(options.file || '', options.source) : null],
-			sourcesContent: options.includeContent ? [this.original] : [null],
+			file: options.file ? options.file.split(/[/\\]/).pop() : undefined,
+			sources: [options.source ? getRelativePath(options.file || '', options.source) : (options.file || '')],
+			sourcesContent: options.includeContent ? [this.original] : undefined,
 			names,
 			mappings: mappings.raw,
 		};