修复使用AnnotationUtil.getAnnotationAlias获取注解时可能会出现空指针的问题

hutool-core/src/main/java/cn/hutool/core/annotation/AnnotationUtil.java

@@ -457,6 +457,9 @@ public class AnnotationUtil {
 	 */
 	public static <T extends Annotation> T getAnnotationAlias(AnnotatedElement annotationEle, Class<T> annotationType) {
 		final T annotation = getAnnotation(annotationEle, annotationType);
+		if (null == annotation) {
+			return null;
+		}
 		return aggregatingFromAnnotation(annotation).synthesize(annotationType);
 	}
 

hutool-core/src/test/java/cn/hutool/core/annotation/AnnotationUtilTest.java

@@ -56,6 +56,14 @@ public class AnnotationUtilTest {
 		Assert.assertTrue(AnnotationUtil.isSynthesizedAnnotation(annotation));
 	}
 
+	@Test
+	public void getAnnotationSyncAliasWhenNotAnnotation() {
+		getAnnotationSyncAlias();
+		// 使用AnnotationUtil.getAnnotationAlias获取对象上并不存在的注解
+		final Alias alias = AnnotationUtil.getAnnotationAlias(ClassWithAnnotation.class, Alias.class);
+		Assert.assertNull(alias);
+	}
+
 	@AnnotationForTest(value = "测试", names = {"测试1", "测试2"})
 	@RepeatAnnotationForTest
 	static class ClassWithAnnotation{