修复EnumUtil空指针问题

hutool-core/src/test/java/org/dromara/hutool/core/util/IssueI9NSZ4Test.java

@@ -0,0 +1,88 @@
+package org.dromara.hutool.core.util;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.ToString;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class IssueI9NSZ4Test {
+	@Test
+	public void getByTest() {
+		// AnimalKindInZoo所有枚举结果的getMappedValue结果值中都无AnimalKind.DOG，返回null
+		final AnimalKindInZoo by = EnumUtil.getBy(AnimalKindInZoo::getMappedValue, AnimalKind.DOG);
+		Assertions.assertNull(by);
+	}
+
+	@Test
+	public void getByTest2() {
+		final AnimalKindInZoo by = EnumUtil.getBy(AnimalKindInZoo::getMappedValue, AnimalKind.BIRD);
+		Assertions.assertEquals(AnimalKindInZoo.BIRD, by);
+	}
+
+	/**
+	 * 动物类型
+	 */
+	@Getter
+	@ToString
+	@AllArgsConstructor
+	public enum AnimalKind {
+
+		/**
+		 * 猫
+		 */
+		CAT("cat", "猫"),
+		/**
+		 * 狗
+		 */
+		DOG("dog", "狗"),
+		/**
+		 * 鸟
+		 */
+		BIRD("bird", "鸟");
+
+		/**
+		 * 键
+		 */
+		private final String key;
+		/**
+		 * 值
+		 */
+		private final String value;
+	}
+
+	/**
+	 * 动物园里的动物类型
+	 */
+	@Getter
+	@ToString
+	@AllArgsConstructor
+	public enum AnimalKindInZoo {
+
+		/**
+		 * 猫
+		 */
+		CAT("cat", "猫", AnimalKind.CAT),
+		/**
+		 * 蛇
+		 */
+		SNAKE("snake", "蛇", null),
+		/**
+		 * 鸟
+		 */
+		BIRD("bird", "鸟", AnimalKind.BIRD);
+
+		/**
+		 * 键
+		 */
+		private final String key;
+		/**
+		 * 值
+		 */
+		private final String value;
+		/**
+		 * 映射值
+		 */
+		private final AnimalKind mappedValue;
+	}
+}