@Override
    public String asString() {
        if (numeric == Tensor.invalidIndex) {
            return null;
        }
        
        // String label for indexed dimension are created at runtime to reduce memory usage.
        if (string == null) {
            return String.valueOf(numeric);
        }
        
        return string;
    }
{@link Label} implementation used by {@link LabelCache}.

@author glebashnik
vespajlib/src/main/java/com/yahoo/tensor/impl/LabelImpl.java