Handle empty tensors

Author: lkdvos

src/tensors/treetransformers.jl

@@ -103,7 +103,7 @@ function _transformer_weight((matrix, structures_dst, structures_src))
 end
 
 function buffersize(transformer::GenericTreeTransformer)
-    return maximum(transformer.data) do (basistransform, structures_dst, _)
+    return maximum(transformer.data; init=0) do (basistransform, structures_dst, _)
         return prod(structures_dst[1][1]) * max(size(basistransform)...)
     end
 end