NPE when generating schema for class with JsonValue annotation over Collection/Array

[peshitz]

When trying to generate jsonSchema for the following class, an NPE is raised.
jackson-databind version is 2.2.3.

public class Histogram{

    ...
    @JsonValue
    public Collection<String> asCollection() {...}

    }

java.lang.NullPointerException
    at com.fasterxml.jackson.databind.ser.std.AsArraySerializerBase.acceptJsonFormatVisitor(AsArraySerializerBase.java:255)
    at com.fasterxml.jackson.databind.ser.std.JsonValueSerializer.acceptJsonFormatVisitor(JsonValueSerializer.java:269)
    at com.fasterxml.jackson.databind.ser.std.JsonValueSerializer.acceptJsonFormatVisitor(JsonValueSerializer.java:269)
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.acceptJsonFormatVisitor(DefaultSerializerProvider.java:281)
    at com.fasterxml.jackson.databind.ObjectMapper.acceptJsonFormatVisitor(ObjectMapper.java:2673)

[cowtowncoder]

Thanks. I assume this also occurs with 2.3.2.

[greyfairer]

Same occurs in 2.3.2 and in 2.4.2.

The problem seems to be in AsArraySerializerBase.java:

    @Override
    public void acceptJsonFormatVisitor(JsonFormatVisitorWrapper visitor, JavaType typeHint)
        throws JsonMappingException
    {
        JsonArrayFormatVisitor arrayVisitor = (visitor == null) ? null : visitor.expectArrayFormat(typeHint);
        if (arrayVisitor != null) {
            TypeFactory tf = visitor.getProvider().getTypeFactory();
            JavaType contentType = tf.moreSpecificType(_elementType, typeHint.getContentType());

Here, typeHint is null for a List/Set used in a @JsonValue

[cowtowncoder]

Fixed this in jackson-databind; added a unit test here and it passes against 2.4.3-SNAPSHOT.
Not planning to backport in 2.3 because change in databind not trivial (want to minimize any chance of regression for 2.3).

[greyfairer]

This bug seems not to be completely fixed. It doesn't throw a NPE anymore, but it doesn't generate the schema correctly either. It just generates:

    {
        "type":"array"
    }

I extended the test to use a collection of nested beans, and expected to see the schema of the nested items, e.g.:

    {
      "type" : "array",
      "items" : {
        "type" : "object",
        "properties" : {
          "property1" : {
            "type" : "integer"
          },
          "property2" : {
            "type" : "string"
          }
        }
      }
    }

See updated test:
greyfairer@2a9b859

[cowtowncoder]

Sounds like related bug (something that was masked by NPE most likely). I'll create a new issue since it may take longer to figure out this problem.