[util] test failure in testString

[olebole]

I just started to update the Debian packages to topcat-4.9.1 & co. (was delayed since Github removed the SVN access which I used to get individual starjava packages). In the "util" package, my build fails in the unit test step with

    [junit] Testcase: testString took 0.007 sec
    [junit] 	FAILED
    [junit] expected:<$[?]?> but was:<$[]?>
    [junit] junit.framework.ComparisonFailure: expected:<$[?]?> but was:<$[]?>
    [junit] 	at junit.framework.Assert.assertEquals(Assert.java:81)
    [junit] 	at junit.framework.Assert.assertEquals(Assert.java:87)
    [junit] 	at uk.ac.starlink.util.PrimitiveListTest.testString(PrimitiveListTest.java:150)
    [junit] 	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    [junit] 	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    [junit] 	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    [junit] 	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    [junit] 	at junit.framework.TestCase.runTest(TestCase.java:164)
    [junit] 	at junit.framework.TestCase.runBare(TestCase.java:130)
    [junit] 	at junit.framework.TestResult$1.protect(TestResult.java:106)
    [junit] 	at junit.framework.TestResult.runProtected(TestResult.java:124)
    [junit] 	at junit.framework.TestResult.run(TestResult.java:109)
    [junit] 	at junit.framework.TestCase.run(TestCase.java:120)
    [junit] 	at junit.framework.TestSuite.runTest(TestSuite.java:230)
    [junit] 	at junit.framework.TestSuite.run(TestSuite.java:225)
    [junit] 	at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.run(JUnitTestRunner.java:535)
    [junit] 	at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.launch(JUnitTestRunner.java:1197)
    [junit] 	at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.main(JUnitTestRunner.java:1042)
    [junit] 

BUILD FAILED
/build/starjava-util-1.0+2024.01.29/build.xml:932: Test uk.ac.starlink.util.PrimitiveListTest failed

which I do not fully understand. The test code here is https://github.com/Starlink/starjava/blob/a4447132ba0f5041f6cf95632575e39ae735e8fd/util/src/testcases/uk/ac/starlink/util/PrimitiveListTest.java#L146-L150

The used SDK is openjdk-17 (17.0.11) on Debian unstable.