@Override
    public Tensor evaluate(EvaluationContext<NAMETYPE> context) {
        Tensor tensor = context.getTensor(name);
        if (tensor == null) return null;
        verifyType(tensor.type());
        return tensor;
    }
A variable tensor which must be compatible with the given type
vespajlib/src/main/java/com/yahoo/tensor/evaluation/VariableTensor.java