Added check for falsey adapter in registerAdapter

src/pawsqlite.mjs

@@ -21,6 +21,10 @@ export default {
     return adapter.delete(dbName);
   },
   registerAdapter: function(adapter) {
+    if (!adapter) {
+      throw new PawSQLiteError("Invalid adapter");
+    }
+
     const wrapped = wrapAdapter(adapter);
 
     if (getAdapter(wrapped.name, true)) {