fix(generate): allow datamodels.type to be undefined

fixes #106

Author: eiten0803

src/generate.ts

@@ -129,7 +129,7 @@ export async function generate(
   }
 
   // Types behaves like model
-  for (const model of datamodel.types) {
+  for (const model of datamodel.types || []) {
     await eventEmitter.emit('Model', model, eventArguments);
   }