private static void readTensorCell(TokenBuffer buffer, Tensor.Builder builder) {
        expectObjectStart(buffer.current());

        TensorAddress address = null;
        Double value = null;
        int initNesting = buffer.nesting();
        for (buffer.next(); buffer.nesting() >= initNesting; buffer.next()) {
            String currentName = buffer.currentName();
            if (TensorReader.TENSOR_ADDRESS.equals(currentName)) {
                address = readAddress(buffer, builder.type());
            } else if (TensorReader.TENSOR_VALUE.equals(currentName)) {
                value = readDouble(buffer);
            }
        }
        expectObjectEnd(buffer.current());
        if (address == null)
            throw new IllegalArgumentException("Expected an object in a tensor 'cells' array to contain an 'address' field");
        if (value == null)
            throw new IllegalArgumentException("Expected an object in a tensor 'cells' array to contain a 'value' field");
        builder.cell(address, value);
    }
Reads the tensor format defined at
See <a href="https://docs.vespa.ai/en/reference/document-json-format.html">https://docs.vespa.ai/en/reference/document-json-format.html</a>

@author geirst
@author bratseth
document/src/main/java/com/yahoo/document/json/readers/TensorReader.java