public static UnboundBuilder of(TensorType type) {
            //TODO Wire in expected map size to avoid expensive resize
            return new UnboundBuilder(type, INITIAL_HASH_CAPACITY);
        }
Temporarily stores all cells to find bounds of indexed dimensions,
then creates a tensor using BoundBuilder. This is due to the
fact that for serialization the size of the dense subspace must be
known, and equal for all dense subspaces. A side effect is that the
tensor type is effectively changed, such that unbound indexed
dimensions become bound.
vespajlib/src/main/java/com/yahoo/tensor/MixedTensor.java