fix: add missing dependency typedoc

Fixes #5

src/common.ts

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2018 StApps
+ * Copyright (C) 2018-2019 StApps
  * This program is free software: you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the Free
  * Software Foundation, version 3.
@@ -129,7 +129,13 @@ export function getProjectReflection(srcPath: PathLike): ProjectReflection {
   const inputFiles = app.expandInputFiles([srcPath.toString()]);
 
   // get project reflection from input files
-  return app.convert(inputFiles);
+  const result = app.convert(inputFiles);
+
+  if (typeof result === 'undefined') {
+    throw new Error('Project reflection could not be generated.');
+  }
+
+  return result;
 }
 
 /**