`null` String for `Exception`s deserialized as String "null" instead of `null`

[ZeleniJure]

Hi!
I have been trying to solve this problem for over a day now, and what research I did showed that this should work, but it does not in my case, e.g. default behaviour should deserialize null objects to null objects, right?

The problem is that while serialization of string object properties with null value is fine, the deserialization is not.

What I want is, if string property value

• is "null" -> deserialize to string "null"
• is null -> deserialize to null object
• is "" -> deserialize to empty string ("")
• is "ladida" -> deserialize to string "ladida"

Example code to reproduce the error:

        final ObjectMapper mapper = new ObjectMapper();
        // so that the error is visible at the beginning of the output :)
        mapper.configure(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY, true);
        final NullPointerException ex = new NullPointerException();
        String json;
        try {
            json = mapper.writeValueAsString(ex);
            System.out.println("OK\t-> " + json);
            final NullPointerException parsed = mapper.readValue(json, NullPointerException.class);
            json = mapper.writeValueAsString(parsed);
            System.out.println("Not OK\t<- " + json);
        } catch (final IOException e1) {
            e1.printStackTrace();
        }

Output:
See 'localizedMessage' and 'message' strings in serialized and deserialized output. Serialization is OK (null), deserialized is not ok (string containing "null")

OK	-> {"cause":null,"localizedMessage":null,"message":null,"stackTrace":[{"className":"com.cosylab.tcs.commons.communication.model.Test","fileName":"Test.java","lineNumber":87,"methodName":"main","nativeMethod":false}],"suppressed":[]}
Not OK	<- {"cause":null,"localizedMessage":"null","message":"null","stackTrace":[{"className":"com.cosylab.tcs.commons.communication.model.Test","fileName":"Test.java","lineNumber":87,"methodName":"main","nativeMethod":false}],"suppressed":[]}

Version: 2.9.1

[cowtowncoder]

Jackson json module does not coerce JSON nulls into String "null" so I am bit surprised by this.

But I think it may be possible that specific deserializer for Exception types might have something, so there may be this one special case. I'll have a look if that explains what you observe.

[cowtowncoder]

Ok yes. Use of parser.getText() unfortunately did include "null" as value. So better choice is parser.getValueAsString() which only coerces scalars, but returns null for JSON null as well as for structured tokens (START_ARRAY, START_OBJECT).

[sanjaybsm]

is this issue fixed, if yes then could you please let us know the version?

[kupci]

According to the doc it was fixed in 2.9.3: https://github.com/FasterXML/jackson-databind/blob/master/release-notes/VERSION-2.x

[cowtowncoder]

@sanjaybsm see the "Milestone" on right side of this page. That is where version information is usually included. Fix is also listed under release-notes/VERSION (or depending on branch, release-notes/VERSION-2.x) as @kupci noted.