Regression in `AbstractMapAssert.containsExactly` causes `NullPointerException`

[sbrannen]

Describe the bug

• assertj core version: 3.25.0

Commit 498ee5b introduced a regression in AbstractMapAssert.containsExactly.

Specifically, it is not always safe to put null into a Map.

assertj/assertj-core/src/main/java/org/assertj/core/internal/Maps.java

Line 589 in 887f97b

emptyMap.put(keyFromActual, null);

Test case reproducing the bug

The following now fails with a NullPointerException.

@Test
void assertJBug() {
	Properties properties = new Properties();
	properties.setProperty("k1", "v1");
	properties.setProperty("k2", "v2");
	assertThat(properties).containsExactly(entry("k1", "v1"), entry("k2", "v2"));
}

[scordio]

Thanks for reporting it and the analysis, @sbrannen!

[sbrannen]

In case anyone else runs into this, you may find the workaround I came up with suitable for your use case as well.

spring-projects/spring-framework@ffddbb5#diff-6f347f5b75cdbb58d65e5ec32c8e3ffe9abf719f50f3bc819ec257296d466aee

Basically, I created a new map (LinkedHashMap in this case) based on the original map (Properties in this case), and the NullPointerException is avoided since LinkedHashMap supports null values.

[scordio]

Team decision: 498ee5b should be reverted and #2165 should be addressed again with the knowledge gathered from this issue.

[sbrannen]

Thanks for the quick turnaround! 👍