Bonsai has no leaves

From BonsaiWIKI

First off, having no leaves may not be a problem.

Deciduous bonsai can be expected to lose their leaves in autumn. The leaves may turn brown, but will fall off the tree on their own. Beech is an exception and may hold onto its brown leaves all winter. Some trees are semi-deciduous, like Chinese Elm, and the leaves may not fall until they are pushed off by new growth.