Merge pull request #24230 from wanderleisouza

* pr/24230:
  Polish "Allow to exclude an empty set of ErrorAttributes"
  Allow to exclude an empty set of ErrorAttributes

Closes gh-24230

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/error/ErrorAttributeOptions.java

@@ -63,8 +63,7 @@ public final class ErrorAttributeOptions {
 	 * @return an {@code ErrorAttributeOptions}
 	 */
 	public ErrorAttributeOptions including(Include... includes) {
-		EnumSet<Include> updated = (this.includes.isEmpty()) ? EnumSet.noneOf(Include.class)
-				: EnumSet.copyOf(this.includes);
+		EnumSet<Include> updated = copyIncludes();
 		updated.addAll(Arrays.asList(includes));
 		return new ErrorAttributeOptions(Collections.unmodifiableSet(updated));
 	}
@@ -76,11 +75,15 @@ public final class ErrorAttributeOptions {
 	 * @return an {@code ErrorAttributeOptions}
 	 */
 	public ErrorAttributeOptions excluding(Include... excludes) {
-		EnumSet<Include> updated = EnumSet.copyOf(this.includes);
+		EnumSet<Include> updated = copyIncludes();
 		updated.removeAll(Arrays.asList(excludes));
 		return new ErrorAttributeOptions(Collections.unmodifiableSet(updated));
 	}
 
+	private EnumSet<Include> copyIncludes() {
+		return (this.includes.isEmpty()) ? EnumSet.noneOf(Include.class) : EnumSet.copyOf(this.includes);
+	}
+
 	/**
 	 * Create an {@code ErrorAttributeOptions} with defaults.
 	 * @return an {@code ErrorAttributeOptions}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/servlet/error/ErrorAttributesOptionsTests.java

+/*
+ * Copyright 2012-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.web.servlet.error;
+
+import java.util.EnumSet;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.web.error.ErrorAttributeOptions;
+import org.springframework.boot.web.error.ErrorAttributeOptions.Include;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link ErrorAttributeOptions}.
+ *
+ * @author Wanderlei Souza
+ * @author Stephane Nicoll
+ */
+class ErrorAttributesOptionsTests {
+
+	@Test
+	void includingFromEmptyAttributesReturnAddedEntry() {
+		ErrorAttributeOptions options = ErrorAttributeOptions.of(EnumSet.noneOf(Include.class));
+		assertThat(options.including(Include.EXCEPTION).getIncludes()).containsOnly(Include.EXCEPTION);
+	}
+
+	@Test
+	void includingFromMatchingAttributesDoesNotModifyOptions() {
+		ErrorAttributeOptions options = ErrorAttributeOptions.of(EnumSet.of(Include.EXCEPTION, Include.STACK_TRACE));
+		assertThat(options.including(Include.EXCEPTION).getIncludes()).containsOnly(Include.EXCEPTION,
+				Include.STACK_TRACE);
+	}
+
+	@Test
+	void excludingFromEmptyAttributesReturnEmptyList() {
+		ErrorAttributeOptions options = ErrorAttributeOptions.of(EnumSet.noneOf(Include.class));
+		assertThat(options.excluding(Include.EXCEPTION).getIncludes()).isEmpty();
+	}
+
+	@Test
+	void excludingFromMatchingAttributesRemoveMatch() {
+		ErrorAttributeOptions options = ErrorAttributeOptions.of(EnumSet.of(Include.EXCEPTION, Include.STACK_TRACE));
+		assertThat(options.excluding(Include.EXCEPTION).getIncludes()).containsOnly(Include.STACK_TRACE);
+	}
+
+}