JTableNested:rebuild() fires a query that selects the primary key column of the table as well as the alias column. So it is assumed that any table (unless its class overrides this function) with a 'nested' structure will contain an alias column. Alas, this is not true. The #__assets table does not have an alias column.

In practice, perhaps this never comes up because JTableAsset never has any reason to call rebuild but it should not be theoretically possible for this to happen either. JTableAsset should either override rebuild or #__assets should have an alias column or JTableNested should properly handle that case that a table does not have an alias column.