Nitrite Database Files

New Features

• Add an exists filter - where("field").exists() matches the documents which have the field, irrespective of its value; where("field").exists().not() matches those which do not.
• A field explicitly set to null is present and matches. This is the case no existing filter could express: eq(null) and notEq(null) cannot tell a missing field apart from one holding null, so "has this document been given a value for this field at all" was not answerable.
• The filter deliberately does not extend ComparableFilter and so always runs as a collection scan. A missing field and a field holding null are stored under the same null key in an index, so an index scan could not tell them apart and would disagree with a collection scan.
• Embedded fields are addressed by their dotted path (where("address.city").exists()), the same way Document.containsField resolves them.

Issue Fixes

• Fix JVM crash (SIGSEGV) in the RocksDB backend when a query pages past the end of a collection
• EntrySet, KeySet and ValueSet close the native RocksIterator the first time hasNext() answers false, but hasNext() is idempotent by contract and a second call reached isValid() on the freed handle. BoundedStream's skip loop exhausts the iterator and then the caller asks once more, so any find(..., skipBy(n)) whose skip exceeds the number of remaining records hit it — an ordinary paging request, not an edge case. The existing catch (AssertionError) only covered the case where assertions are enabled (-ea), which is how the tests ran but not how an application runs: without assertions the same call is a SIGSEGV in Java_org_rocksdb_RocksIterator_isValid0Jni that takes the whole process down.
• hasNext() now returns false when the iterator no longer owns its handle, so it never touches a closed iterator and stays idempotent.