public Builder add(String label) {
            var mappedSubtype = type.mappedSubtype();
            if (mappedSubtype.rank() != 1)
                throw new IllegalArgumentException("Cannot add a label without explicit dimension to a tensor of type " +
                                                   type + ": Must have exactly one mapped dimension");
            add(mappedSubtype.dimensions().get(0).name(), label);
            return this;
        }
Adds the label to the only mapped dimension of this.

@throws IllegalArgumentException if this does not have exactly one dimension
vespajlib/src/main/java/com/yahoo/tensor/TensorAddress.java