Deserialize ArrayList from String using Jackson ACCEPT_SINGLE_VALUE_AS_ARRAY

Problem Deserializing array as string with Jackson 2

This is a similar problem to Deserialize ArrayList from String using Jackson

The incoming JSON (which I can't control) has an element 'thelist' which is an array. However, sometimes this comes in as an empty string instead of an array:

eg. instead of "thelist" : [ ]
it comes in as "thelist" : ""

I'm having trouble parsing both cases.

The 'sample.json' file which works fine:

{
   "name" : "widget",
   "thelist" : 
    [
       {"height":"ht1","width":"wd1"}, 
       {"height":"ht2","width":"wd2"}
    ]
}

The classes:

public class Product { 
    private String name; 
    private List<Things> thelist; 
    // with normal getters and setters not shown
}

public class Things {
        String height;
        String width;
        // with normal getters and setters not shown
}

The code that works fine:

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Test2 {
 public static void main(String[] args) 
    {
        ObjectMapper mapper = new ObjectMapper(); 
        Product product = mapper.readValue( new File("sample.json"), Product.class);
    }
}

However, when the JSON has got an empty string instead of an array, ie. "thelist" : ""
I get this error:

com.fasterxml.jackson.databind.JsonMappingException: Can not instantiate value of type [collection type; class java.util.ArrayList, contains [simple type, class com.test.Things]] from JSON String; no single-String constructor