Fixed QualifierAnnotationAutowireCandidateResolver's detection of custom qualifier annotations

Issue: SPR-10107

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

@@ -69,6 +69,21 @@ public abstract class StringUtils {
 	// General convenience methods for working with Strings
 	//---------------------------------------------------------------------
 
+	/**
+	 * Check whether the given String is empty.
+	 * <p>This method accepts any Object as an argument, comparing it to
+	 * <code>null</code> and the empty String. As a consequence, this method
+	 * will never return <code>true</code> for a non-null non-String object.
+	 * <p>The Object signature is useful for general attribute handling code
+	 * that commonly deals with Strings but generally has to iterate over
+	 * Objects since attributes may e.g. be primitive value objects as well.
+	 * @param str the candidate String
+	 * @since 3.2.1
+	 */
+	public static boolean isEmpty(Object str) {
+		return (str == null || "".equals(str));
+	}
+
 	/**
 	 * Check that the given CharSequence is neither <code>null</code> nor of length 0.
 	 * Note: Will return <code>true</code> for a CharSequence that purely consists of whitespace.