Probably - Groovy Spock 2.4 has a bug in MockitoMockMakerImpl.asMockOrNull() — it passes null objects directly to Mockito's WeakConcurrentMap.get() without a null check

[yuriyslobodchikovrc]

Hello!
Here is Claude Code tries to describe reason why tests are failing using combination of versions newer 2.4-M4-groovy-4.0 with mockito and groovy
may be it is wrong:

Groovy 5.x blocked by: Groovy Spock 2.4 has a bug in MockitoMockMakerImpl.asMockOrNull() — it passes null objects directly to Mockito's WeakConcurrentMap.get() without a null check, causing
NPE. The M4 milestone didn't have this MockitoMockMaker feature. .. Groovy 5 upgrade needs to wait for a
Spock patch release (2.4.1+).

" Now I see it clearly. Both M4 and stable call setInteraction() from MockInteraction constructor at offset 99, and both versions end up calling asMockOrNull. But the key difference is in
TargetConstraint.setInteraction():

• M4: isMock(target) → if true → asMock(target). The isMock() calls asMockOrNull() too, but the guard is isRequired() at offset 6-11. The NPE would only happen when the interaction is
  required (1 * ...). For stubs (>>) it's not required, so M4 skips the whole block.
• Stable: calls asMockOrNull(target) unconditionally — no isRequired() guard. So even stubs (>>) trigger the mock maker registry query.

That's the root cause: stable removed the isRequired() guard, so stubs now also call asMockOrNull, which hits the MockitoMockMaker NPE on null targets.

Bottom line: M4 is the correct choice. The Spock 2.4 stable changed TargetConstraint to always query mock makers, exposing the MockitoMockMaker null-handling bug. Staying on Groovy 4.0.31 +
Spock 2.4-M4-groovy-4.0 is correct. "

[yuriyslobodchikovrc]

Of cause AI can hallucinate

[Vampire]

Yes, so why are you only sharing what AI yaps, instead of or at least in addition to a proper techincally 100% correct stacktrace? ;-)

[yuriyslobodchikovrc]

spock-mockito-bug-demo.zip

here is example of working when 2.4-M4-groovy-4.0 is used

`class SpockMockitoNpeBugTest extends Specification {

interface Parent {
    Child getChild()
}

interface Child {
    String getName()
}

def "NPE when stubbing method on null returned from unstubbed mock chain"() {
    given:
    def parent = Mock(Parent)
    // parent.getChild() is not stubbed, so it returns null
    def child = parent.getChild()

    when:
    // This line triggers the bug:
    // Spock 2.4 stable calls asMockOrNull(child) where child is null,
    // MockitoMockMaker passes null to Mockito's getHandler(), NPE
    child.getName() >> "Alice"

    then:
    true
}

}`

[yuriyslobodchikovrc]

and failing with
2.4-groovy-4.0

OpenJDK 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended [ERROR] Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.537 s <<< FAILURE! -- in SpockMockitoNpeBugTest [ERROR] SpockMockitoNpeBugTest.NPE when stubbing method on null returned from unstubbed mock chain -- Time elapsed: 0.530 s <<< ERROR! java.lang.NullPointerException at org.mockito.internal.util.concurrent.WeakConcurrentMap.get(WeakConcurrentMap.java:57) at org.mockito.internal.creation.bytebuddy.InlineDelegateByteBuddyMockMaker.getHandler(InlineDelegateByteBuddyMockMaker.java:522) at org.mockito.internal.creation.bytebuddy.InlineByteBuddyMockMaker.getHandler(InlineByteBuddyMockMaker.java:67) at org.spockframework.mock.runtime.mockito.MockitoMockMakerImpl.asMockOrNull(MockitoMockMakerImpl.java:89) at org.spockframework.mock.runtime.mockito.MockitoMockMaker.asMockOrNull(MockitoMockMaker.java:76) at org.spockframework.mock.runtime.MockMakerRegistry.asMockOrNull(MockMakerRegistry.java:190) at org.spockframework.mock.MockUtil.asMockOrNull(MockUtil.java:85) at org.spockframework.mock.constraint.TargetConstraint.setInteraction(TargetConstraint.java:54) at org.spockframework.mock.runtime.MockInteraction.<init>(MockInteraction.java:61) at org.spockframework.mock.runtime.InteractionBuilder.build(InteractionBuilder.java:187) at SpockMockitoNpeBugTest.NPE when stubbing method on null returned from unstubbed mock chain(SpockMockitoNpeBugTest.groovy:51) [INFO] [INFO] Results: [INFO] [ERROR] Errors: [ERROR] SpockMockitoNpeBugTest.NPE when stubbing method on null returned from unstubbed mock chain:51 » NullPointer [INFO] [ERROR] Tests run: 1, Failures: 0, Errors: 1, Skipped: 0 [INFO]

[AndreasTu]

I can reproduce the issue.
I have created #2337 for the problem.
Thanks for reporting.

Please note that the interaction
child.getName() >> "Alice" does not make sense on a null object, also after fixing #2337.

[yuriyslobodchikovrc]

@AndreasTu
Thank you!

Looks like in my real case I should rewrite old test from

`def brand = servicePlan.getBrand()

brand.getBrandId() >> brandId `

to

' servicePlan.getBrand() >> Brand.builder().brandId(brandId).build() '

and it work for 2.4-groovy-4.0

So may be it was not real bug but could be avoided with better style mocking