Only non-null input resets scheme specific part

Closes gh-24444

spring-web/src/test/java/org/springframework/web/util/UriComponentsBuilderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -769,6 +769,21 @@ public class UriComponentsBuilderTests {
 		assertThat(uriComponents.getQueryParams().get("bar").get(0)).isNull();
 	}
 
+	@Test // gh-24444
+	public void opaqueUriDoesNotResetOnNullInput() throws URISyntaxException {
+		URI uri = new URI("urn:ietf:wg:oauth:2.0:oob");
+		UriComponents result = UriComponentsBuilder.fromUri(uri)
+				.host(null)
+				.port(-1)
+				.port(null)
+				.queryParams(null)
+				.replaceQuery(null)
+				.query(null)
+				.build();
+
+		assertThat(result.toUri()).isEqualTo(uri);
+	}
+
 	@Test
 	public void relativeUrls() {
 		String baseUrl = "https://example.com";