I am using Basex 8.4.4 through the JAVA API and I noticed quite a few occurrences of the following NPE and AIOOB exceptions in the logs:

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java.lang.NullPointerException
        at org.basex.data.DiskData.write(DiskData.java:126)
        at org.basex.data.DiskData.close(DiskData.java:140)
        at org.basex.core.Datas.close(Datas.java:84)
        at org.basex.core.Context.close(Context.java:155)

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org.basex.core.BaseXException: Improper use? Potential bug? Your feedback is welcome:
Contact: basex-talk@mailman.uni-konstanz.de
Version: BaseX 8.4.4
Java: Oracle Corporation, 1.8.0_66
OS: Linux, amd64
Stack Trace:
java.lang.NullPointerException
        at org.basex.data.DiskData.write(DiskData.java:120)
        at org.basex.data.DiskData.flush(DiskData.java:235)
        at org.basex.data.DiskData.finishUpdate(DiskData.java:225)
        at org.basex.core.Command.finishUpdate(Command.java:341)
        at org.basex.core.cmd.ACreate.finishUpdate(ACreate.java:87)
        at org.basex.core.cmd.Replace.run(Replace.java:59)
        at org.basex.core.Command.run(Command.java:398)
        at org.basex.core.Command.execute(Command.java:100)
        at org.basex.core.Command.execute(Command.java:123)

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org.basex.core.BaseXException: Improper use? Potential bug? Your feedback is welcome:
Contact: basex-talk@mailman.uni-konstanz.de
Version: BaseX 8.4.4
Java: Oracle Corporation, 1.8.0_66
OS: Linux, amd64
Stack Trace:
java.lang.ArrayIndexOutOfBoundsException: 0
    at org.basex.io.random.TableDiskAccess.fpre(TableDiskAccess.java:501)
    at org.basex.io.random.TableDiskAccess.setPage(TableDiskAccess.java:473)
    at org.basex.io.random.TableDiskAccess.readPage(TableDiskAccess.java:482)
    at org.basex.io.random.TableDiskAccess.insert(TableDiskAccess.java:316)
    at org.basex.data.Data.insert(Data.java:901)
    at org.basex.data.Data.insert(Data.java:727)
    at org.basex.query.up.atomic.Insert.apply(Insert.java:44)
    at org.basex.query.up.atomic.AtomicUpdateCache.applyUpdates(AtomicUpdateCache.java:297)
    at org.basex.query.up.atomic.AtomicUpdateCache.execute(AtomicUpdateCache.java:281)
    at org.basex.core.cmd.Replace.replace(Replace.java:106)
    at org.basex.core.cmd.Replace.run(Replace.java:57)
    at org.basex.core.Command.run(Command.java:398)
    at org.basex.core.Command.execute(Command.java:100)
    at org.basex.core.Command.execute(Command.java:123)

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The collection files are stored to NFS, but the above exceptions seem to appear at random while trying to update an existing collection.