fix(Repository): default empty dates to null

BREAKING CHANGE: this change makes it so that the date value will no longer be a Date instance based on null, but instead will just be null.

src/repository.js

@@ -229,7 +229,13 @@ export class Repository {
       let value = data[key];
 
       if (entityMetadata.has('types', key)) {
-        populatedData[key] = typer.cast(value, entityMetadata.fetch('types', key));
+        if (dataType === 'date' || dataType === 'datetime') {
+          if (value) {
+            populatedData[key] = typer.default.cast(value, dataType);
+          }
+        } else {
+          populatedData[key] = typer.cast(value, entityMetadata.fetch('types', key));
+        }
 
         continue;
       }