`ParameterBindingJsonReader` fails with NPE when a bindable value for `ObjectId` parameter is `null`

[Matin69]

In JSON queries when you have a nullable value for an object id parameter, A null pointer exception will be thrown. It may seem reasonable but it's not suitable for a case where you want to implement a search function using nullable parameter values. If the value is null you expect null to be replaced with object id.
My case :

    @Query("{ $and : [ { $or : [ { $expr: { $eq: ['?0', 'null'] } } , { movie_id : ObjectId(?0) } ] }, { $or : [ { $expr: { $eq: ['?1', 'null'] } } , { email : ?1 } ] } ] }")
    List<Comment> search(String movieId, String email, Pageable pageable);

The exception :

java.lang.NullPointerException: Cannot invoke "Object.toString()" because the return value of "org.springframework.data.mongodb.util.json.ParameterBindingJsonReader$BindableValue.getValue()" is null
	at org.springframework.data.mongodb.util.json.ParameterBindingJsonReader.readStringFromExtendedJson(ParameterBindingJsonReader.java:1428) ~[spring-data-mongodb-4.0.0.jar:4.0.0]

At least a better exception with a good message should be thrown because it takes some time for me to find out the exception reason

[christophstrobl]

sounds like a bug - thanks for reporting - we'll look into it!

[Matin69]

sounds like a bug - thanks for reporting - we'll look into it!

I opened a pull request that throws an exception with a good message in cases when a bindable value for string parameters is null

[christophstrobl]

thanks @Matin69!

[christophstrobl]

After having a 2nd look at the issue I do think that ParameterBindingJsonReader#readStringFromExtendedJson should be changed to avoid the NPE and return null if the bindable parameter value is actually null.
However, ObjectId(?0) should throw an IllegalArgumentException in case the parameter value is null aligning the behaviour to new ObjectId((String) null).