NPE with extracting(Function... extractors)

[stanio]

Assertions using extracting(Function... extractors) over an actual null object/reference fail with NullPointerException:

java.lang.NullPointerException
	at org.assertj.core.api.AbstractObjectAssert.lambda$extractingForProxy$0(AbstractObjectAssert.java:926)
	at java.base/...
	at org.assertj.core.api.AbstractObjectAssert.extractingForProxy(AbstractObjectAssert.java:927)
	at org.assertj.core.api.AbstractObjectAssert.extracting(AbstractObjectAssert.java:917)

• assertj core version: 3.25.3
• java version: 8, 11, 17, 21
• test framework version: junit5

Test case reproducing the bug

import static org.assertj.core.api.Assertions.assertThat;

import java.awt.geom.Point2D;

import org.junit.jupiter.api.Test;

    @Test
    void verifyCoordinates() {
        Point2D point = null; //new Point(5, 3);
    
        assertThat(point).as("point")
                .extracting(Point2D::getX, Point2D::getY)
                .as("x, y")
                .containsExactly(5.0, 3.0);
    }

For comparison, using extracting(String... propertiesOrFields):

    assertThat(point).as("point")
            .extracting("x", "y")
            .as("x, y")
            .containsExactly(5.0, 3.0);

yields:

java.lang.IllegalArgumentException: The object to extract fields/properties from should not be null
	at org.assertj.core.util.Preconditions.checkArgument(Preconditions.java:131)
	at org.assertj.core.extractor.ByNameMultipleExtractor.apply(ByNameMultipleExtractor.java:36)
	at org.assertj.core.extractor.ByNameMultipleExtractor.apply(ByNameMultipleExtractor.java:24)
	at org.assertj.core.api.AbstractObjectAssert.extracting(AbstractObjectAssert.java:789)

I think the former usage should match the latter behavior.

[stanio]

I have found the following related issues: #2392 (comment), #2401, #2495. Not sure if the last is meant to address this more specific one.

[stanio]

I think the former usage should match the latter behavior.

Or more likely, both should match:

        Point2D point = null;

        assertThat(point).as("point").isNotNull()
                .extracting(...

java.lang.AssertionError: [point] 
Expecting actual not to be null

[joel-costigliola]

I agree we could be more consistent there