Hi Christian,
    I am using  basex-xqj client, XQExpression-8.executeQuery() API throws java.lang.NullPointerException exception while executing XQuery(retrieving the 171 MB xml document) like db:open('testenvSSL1', '6300000180000114/0600000180002931.xml'), marked in red below. 

Could you please help me to fix this java.lang.NullPointerException exception issue? 

Source code:
===========
final XQExpression xqpe = m_conn.createExpression();
String query = "db:open('" + databaseName + "', '" + pathURL + "')";
   final XQResultSequence resultSeq = xqpe.executeQuery(query);      

pom.xml:
========
<!-- https://mvnrepository.com/artifact/net.xqj/basex-xqj -->
<dependency>
    <groupId>net.xqj</groupId>
    <artifactId>basex-xqj</artifactId>
    <version>9.0</version>
</dependency>
        <dependency>
            <groupId>com.xqj2</groupId>
            <artifactId>xqj2</artifactId>
            <version>0.2.0</version>
        </dependency>
        <dependency>
            <groupId>javax.xml.xquery</groupId>
            <artifactId>xqj-api</artifactId>
            <version>1.0</version>
        </dependency>

Retrieve of 8 MB xml document successful working log:
===================================================
2020-08-27 10:04:12,040 INFO  [stdout] (default task-3) [10:04:12.040] TRACE: XQConnection-1.createExpression() invoked.

2020-08-27 10:04:12,040 INFO  [stdout] (default task-3) [10:04:12.040] TRACE: XQConnection.getStaticContext() invoked.

2020-08-27 10:04:12,056 INFO  [stdout] (default task-3) [10:04:12.040] TRACE: XQExpression-4.executeQuery(), raw XQuery resolved to: db:open('testenvSSL1', '6300000180000114/0600000180002930.xml')

2020-08-27 10:04:12,650 INFO  [stdout] (default task-3) [10:04:12.650] DEBUG: XQExpression-4.close() invoked.


Upload 171 MB xml document successful log:
========================================

2020-08-27 10:06:31,552 INFO  [stdout] (default task-3) [10:06:31.552] TRACE: XQConnection-1.createExpression() invoked.

2020-08-27 10:06:31,552 INFO  [stdout] (default task-3) [10:06:31.552] TRACE: XQConnection.getStaticContext() invoked.

2020-08-27 10:06:31,568 INFO  [stdout] (default task-3) [10:06:31.552] TRACE: XQExpression-6.executeQuery(), raw XQuery resolved to: db:replace('testenvSSL1', '6300000180000114/0600000180002931.xml', 'C:\Program Files (x86)\BaseX\data\0600000180002931.xml')

2020-08-27 10:06:40,896 INFO  [stdout] (default task-3) [10:06:40.896] DEBUG: XQExpression-6.close() invoked.


Retrieve of 171 MB xml document failed, nonworking log:
=========================================================
2020-08-27 10:06:45,161 INFO  [stdout] (default task-3) [10:06:45.161] TRACE: XQConnection-1.createExpression() invoked.

2020-08-27 10:06:45,161 INFO  [stdout] (default task-3) [10:06:45.161] TRACE: XQConnection.getStaticContext() invoked.

2020-08-27 10:06:45,161 INFO  [stdout] (default task-3) [10:06:45.161] TRACE: XQExpression-8.executeQuery(), raw XQuery resolved to: db:open('testenvSSL1', '6300000180000114/0600000180002931.xml')

2020-08-27 10:06:53,083 ERROR [org.springframework.boot.web.servlet.support.ErrorPageFilter] (default task-3) Forwarding to error page from request [/servlet/XMLStoreServiceServlet] due to exception [null]: java.lang.NullPointerException



referred source code from:
https://github.com/BaseXdb/basex/tree/master/basex-examples/src/main/java/org/basex/examples/xqj

Thanks,
Srikumar