`@Aggregation` repository query method causes `NullPointerException` when the result is empty

[rootdavinalfa]

Hello,

i'm have an issue regarding usage of Aggregation annotation on spring-data-mongodb

What i'm encounter is

Cannot invoke "org.bson.Document.isEmpty()" because "source" is null

This happen when collection empty (not have any document) but if have an document, i'm not encounter the error.

Here some snippet of code i'm using:

@Aggregation(
        "{" +
                "\$project: { maxid: {\$max: '\$_id'} }" +
                "}"
    )
    fun getMaxUnitID(): String?

[christophstrobl]

Thanks for reporting - seems we miss a null check in AggregationUtils.