@Override
    public Double getAsDouble(TensorAddress address) {
        var block = index.blockOf(address);
        int denseOffset = index.denseOffsetOf(address);
        if (block == null || denseOffset < 0 || denseOffset >= block.cells.length) {
            return null;
        }
        return block.cells[denseOffset];
    }
Returns the value at the given address
vespajlib/src/main/java/com/yahoo/tensor/MixedTensor.java