thanks for the PR @quaff but what's the rationale behind this?

using the getTitle() over this.title isn't that much of an improvement because if the field is not set, the getter derives the result from the this.status field (namely, the reason phrase of the enum which is constant). since this.status already participates in both equals() and hashcode(), this change doesn't add new information to these methods.

it even arguably can make them less performant, because now instead of a simple null equality + int comparison, it adds resolution of an enum from the status code + getting the enum's reason phrase to the mix.

so overall I don't see the benefit of this change.

You can review the test I added, currently the ProblemDetail is not equal after serialize then deserialize.
The actual use case is:

		ResponseEntity<ProblemDetail> resp = this.testRestTemplate.exchange(
				RequestEntity.method(HttpMethod.GET, path).header(HttpHeaders.ACCEPT, MediaType.APPLICATION_JSON_VALUE).build(),
				ProblemDetail.class);
		ProblemDetail expected = ProblemDetail.forStatusAndDetail(HttpStatus.CONFLICT, "Conflicts arise");
		expected.setTitle(HttpStatus.CONFLICT.getReasonPhrase());
		expected.setInstance(URI.create(path));
		assertThat(resp.getBody()).isEqualTo(expected);

Title must be explicit set before comparison, but it is implicit at server side, that's not idiomatic.