Ignore empty entries when parsing MediaTypes and MimeTypes

Prior to Spring Framework 5.1.3, MimeTypeUtils.parseMimeTypes() and
MediaType.parseMediaTypes() ignored empty entries, but 5.1.3 introduced
a regression in that an empty entry -- for example, due to a trailing
comma in the list of media types in an HTTP Accept header -- would result
in a "406 Not Acceptable" response status.

This commit fixes this by filtering out empty entries before parsing
them into MimeType and MediaType instances. Empty entries are therefore
effectively ignored.

Fixes gh-23241

spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java

@@ -38,6 +38,7 @@ import org.springframework.lang.Nullable;
  * @author Arjen Poutsma
  * @author Rossen Stoyanchev
  * @author Dimitrios Liapis
+ * @author Sam Brannen
  * @since 4.0
  */
 public abstract class MimeTypeUtils {
@@ -259,10 +260,11 @@ public abstract class MimeTypeUtils {
 			return Collections.emptyList();
 		}
 		return tokenize(mimeTypes).stream()
-				.map(MimeTypeUtils::parseMimeType).collect(Collectors.toList());
+				.filter(StringUtils::hasText)
+				.map(MimeTypeUtils::parseMimeType)
+				.collect(Collectors.toList());
 	}
 
-
 	/**
 	 * Tokenize the given comma-separated string of {@code MimeType} objects
 	 * into a {@code List<String>}. Unlike simple tokenization by ",", this