Merge pull request #14252 from Microsoft/master-fix12297

[Master] Fix 12297 undefined exception in writeReferencePath

Author: yuit

src/compiler/utilities.ts

@@ -2675,7 +2675,7 @@ namespace ts {
             if (sourceFiles.length) {
                 const jsFilePath = options.outFile || options.out;
                 const sourceMapFilePath = getSourceMapFilePath(jsFilePath, options);
-                const declarationFilePath = options.declaration ? removeFileExtension(jsFilePath) + ".d.ts" : undefined;
+                const declarationFilePath = options.declaration ? removeFileExtension(jsFilePath) + ".d.ts" : "";
                 action({ jsFilePath, sourceMapFilePath, declarationFilePath }, createBundle(sourceFiles), emitOnlyDtsFiles);
             }
         }