Allow null argument for `ResponseEntity.DefaultBuilder.eTag(String etag)`

[abremora]

Affects: v5.3.22

Description

Building a response with etags can result in a NullPointerException if the argument for etag is null. Surprisingly, HttpHeaders.setETag(@Nullable String etag) handles null arguments and is called in ResponseEntity.DefaultBuilder.eTag(String etag).

Sample Code

    var response = ResponseEntity
        .ok()
        .eTag(null)
        .body(body);

Effected Code

spring-framework/spring-web/src/main/java/org/springframework/http/ResponseEntity.java

Lines 565 to 574 in b72ee5f

	public BodyBuilder eTag(String etag) {
	if (!etag.startsWith("\"") && !etag.startsWith("W/\"")) {
	etag = "\"" + etag;
	}
	if (!etag.endsWith("\"")) {
	etag = etag + "\"";
	}
	this.headers.setETag(etag);
	return this;
	}

spring-framework/spring-web/src/main/java/org/springframework/http/HttpHeaders.java

Lines 1042 to 1052 in b72ee5f

	public void setETag(@Nullable String etag) {
	if (etag != null) {
	Assert.isTrue(etag.startsWith("\"") || etag.startsWith("W/"),
	"Invalid ETag: does not start with W/ or \"");
	Assert.isTrue(etag.endsWith("\""), "Invalid ETag: does not end with \"");
	set(ETAG, etag);
	}
	else {
	remove(ETAG);
	}
	}

Solution

• Allow null strings
• remove etag for null strings (like HttpHeaders.setETag() already does)

Therefore it should be safe just to call HttpHeaders.setETag() for null values:

public BodyBuilder eTag(String etag) {
	if (etag != null && !etag.startsWith("\"") && !etag.startsWith("W/\"")) {
		etag = "\"" + etag;
	}
	if (etag != null && !etag.endsWith("\"")) {
		etag = etag + "\"";
	}
	this.headers.setETag(etag);
	return this;
}