protected int requiredNextStopCharIndex(int pos) {
            pos = stopCharIndex(pos);
            if (pos == string.length()) {
                throw new IllegalArgumentException("Malformed tensor string '" + string +
                                                   "': Expected a ',', ']' or '}', ':' after position " + pos);
            }
            return pos;
        }
Derives the tensor type from the first address string in the given tensor string
vespajlib/src/main/java/com/yahoo/tensor/TensorParser.java