UriComponentsBuilder parse of empty fragments

Check for an empty fragment in UriComponentsBuilder.fromUriString(...)
to prevent the invocation of fragment(...).

Previously, UriComponentsBuilder.fromUriString(...) threw an exception
in the case of an empty fragment being provided (e.g. /example#).

Issue: SPR-10363

spring-web/src/main/java/org/springframework/web/util/UriComponentsBuilder.java

@@ -48,6 +48,7 @@
  * @author Arjen Poutsma
  * @author Rossen Stoyanchev
  * @author Phillip Webb
+ * @author Oliver Gierke
  * @since 3.1
  * @see #newInstance()
  * @see #fromPath(String)
@@ -204,7 +205,10 @@ public static UriComponentsBuilder fromUriString(String uri) {
 				builder.path(path);
 				builder.query(query);
 			}
-			builder.fragment(fragment);
+
+			if (StringUtils.hasText(fragment)) {
+				builder.fragment(fragment);
+			}
 
 			return builder;
 		}

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

@@ -23,16 +23,16 @@
 import java.util.Map;
 
 import org.junit.Test;
-
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 
-import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.*;
 import static org.junit.Assert.*;
 
 /**
  * @author Arjen Poutsma
  * @author Phillip Webb
+ * @author Oliver Gierke
  */
 public class UriComponentsBuilderTests {
 
@@ -354,4 +354,11 @@ public void emptySegments() throws Exception {
 		assertThat(UriComponentsBuilder.fromUriString("http://example.com/abc/").path("/x/").path("/y/z").build().toString(), equalTo("http://example.com/abc/x/y/z"));
 		assertThat(UriComponentsBuilder.fromUriString("http://example.com/abc/").pathSegment("x").path("y").build().toString(), equalTo("http://example.com/abc/x/y"));
 	}
+
+	@Test
+	public void parsesEmptyFragment() {
+		UriComponents components = UriComponentsBuilder.fromUriString("/example#").build();
+		assertThat(components.getFragment(), is(nullValue()));
+		assertThat(components.toString(), equalTo("/example"));
+	}
 }