Ignore empty values in config location properties

This commit updates config data property binding to ignore empty
elements in `spring.config.location` and `spring.config.import`
property values when a value is a comma-delimited string
representing a collection.

Fixes gh-26342

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataLocationBindHandler.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -16,7 +16,10 @@
 
 package org.springframework.boot.context.config;
 
+import java.util.Arrays;
 import java.util.List;
+import java.util.Objects;
+import java.util.stream.Collectors;
 
 import org.springframework.boot.context.properties.bind.AbstractBindHandler;
 import org.springframework.boot.context.properties.bind.BindContext;
@@ -30,6 +33,7 @@ import org.springframework.boot.origin.Origin;
  * objects.
  *
  * @author Phillip Webb
+ * @author Scott Frederick
  */
 class ConfigDataLocationBindHandler extends AbstractBindHandler {
 
@@ -40,19 +44,22 @@ class ConfigDataLocationBindHandler extends AbstractBindHandler {
 			return withOrigin(context, (ConfigDataLocation) result);
 		}
 		if (result instanceof List) {
-			List<Object> list = (List<Object>) result;
+			List<Object> list = ((List<Object>) result).stream().filter(Objects::nonNull).collect(Collectors.toList());
 			for (int i = 0; i < list.size(); i++) {
 				Object element = list.get(i);
 				if (element instanceof ConfigDataLocation) {
 					list.set(i, withOrigin(context, (ConfigDataLocation) element));
 				}
 			}
+			return list;
 		}
 		if (result instanceof ConfigDataLocation[]) {
-			ConfigDataLocation[] locations = (ConfigDataLocation[]) result;
+			ConfigDataLocation[] locations = Arrays.stream((ConfigDataLocation[]) result).filter(Objects::nonNull)
+					.toArray(ConfigDataLocation[]::new);
 			for (int i = 0; i < locations.length; i++) {
 				locations[i] = withOrigin(context, locations[i]);
 			}
+			return locations;
 		}
 		return result;
 	}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/config/ConfigDataEnvironmentContributorTests.java

@@ -43,13 +43,14 @@ import static org.mockito.Mockito.mock;
  *
  * @author Phillip Webb
  * @author Madhura Bhave
+ * @author Scott Frederick
  */
 class ConfigDataEnvironmentContributorTests {
 
 	private static final ConfigDataLocation TEST_LOCATION = ConfigDataLocation.of("test");
 
-	private ConfigDataActivationContext activationContext = new ConfigDataActivationContext(CloudPlatform.KUBERNETES,
-			null);
+	private final ConfigDataActivationContext activationContext = new ConfigDataActivationContext(
+			CloudPlatform.KUBERNETES, null);
 
 	@Test
 	void getKindReturnsKind() {
@@ -125,6 +126,16 @@ class ConfigDataEnvironmentContributorTests {
 				ConfigDataLocation.of("boot"));
 	}
 
+	@Test
+	void getImportsIgnoresEmptyElements() {
+		MockPropertySource propertySource = new MockPropertySource();
+		propertySource.setProperty("spring.config.import", "spring,,boot,");
+		ConfigData configData = new ConfigData(Collections.singleton(propertySource));
+		ConfigDataEnvironmentContributor contributor = createBoundContributor(null, configData, 0);
+		assertThat(contributor.getImports()).containsExactly(ConfigDataLocation.of("spring"),
+				ConfigDataLocation.of("boot"));
+	}
+
 	@Test
 	void hasUnprocessedImportsWhenNoImportsReturnsFalse() {
 		ConfigData configData = new ConfigData(Collections.singleton(new MockPropertySource()));
@@ -205,9 +216,9 @@ class ConfigDataEnvironmentContributorTests {
 				"classpath:application-profile.properties");
 		ConfigDataEnvironmentContributor classpathImports = createBoundContributor("classpath:/");
 		classpathImports = classpathImports.withChildren(ImportPhase.BEFORE_PROFILE_ACTIVATION,
-				Arrays.asList(classpathApplication));
+				Collections.singletonList(classpathApplication));
 		classpathImports = classpathImports.withChildren(ImportPhase.AFTER_PROFILE_ACTIVATION,
-				Arrays.asList(classpathProfile));
+				Collections.singletonList(classpathProfile));
 		ConfigDataEnvironmentContributor root = createBoundContributor("root");
 		root = root.withChildren(ImportPhase.BEFORE_PROFILE_ACTIVATION, Arrays.asList(fileImports, classpathImports));
 		assertThat(asLocationsList(root.iterator())).containsExactly("file:application-profile.properties",

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/config/ConfigDataLocationBindHandlerTests.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -30,6 +30,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Tests for {@link ConfigDataLocationBindHandler}.
  *
  * @author Phillip Webb
+ * @author Scott Frederick
  */
 class ConfigDataLocationBindHandlerTests {
 
@@ -54,6 +55,21 @@ class ConfigDataLocationBindHandlerTests {
 		assertThat(bound[2].getOrigin()).hasToString(expectedLocation);
 	}
 
+	@Test
+	void bindToArrayFromCommaStringPropertyIgnoresEmptyElements() {
+		MapConfigurationPropertySource source = new MapConfigurationPropertySource();
+		source.put("locations", ",a,,b,c,");
+		Binder binder = new Binder(source);
+		ConfigDataLocation[] bound = binder.bind("locations", ARRAY, this.handler).get();
+		String expectedLocation = "\"locations\" from property source \"source\"";
+		assertThat(bound[0]).hasToString("a");
+		assertThat(bound[0].getOrigin()).hasToString(expectedLocation);
+		assertThat(bound[1]).hasToString("b");
+		assertThat(bound[1].getOrigin()).hasToString(expectedLocation);
+		assertThat(bound[2]).hasToString("c");
+		assertThat(bound[2].getOrigin()).hasToString(expectedLocation);
+	}
+
 	@Test
 	void bindToArrayFromIndexedPropertiesSetsOrigin() {
 		MapConfigurationPropertySource source = new MapConfigurationPropertySource();
@@ -85,6 +101,21 @@ class ConfigDataLocationBindHandlerTests {
 		assertThat(bound.getLocation(2).getOrigin()).hasToString(expectedLocation);
 	}
 
+	@Test
+	void bindToValueObjectFromCommaStringPropertyIgnoresEmptyElements() {
+		MapConfigurationPropertySource source = new MapConfigurationPropertySource();
+		source.put("test.locations", ",a,b,,c,");
+		Binder binder = new Binder(source);
+		ValueObject bound = binder.bind("test", VALUE_OBJECT, this.handler).get();
+		String expectedLocation = "\"test.locations\" from property source \"source\"";
+		assertThat(bound.getLocation(0)).hasToString("a");
+		assertThat(bound.getLocation(0).getOrigin()).hasToString(expectedLocation);
+		assertThat(bound.getLocation(1)).hasToString("b");
+		assertThat(bound.getLocation(1).getOrigin()).hasToString(expectedLocation);
+		assertThat(bound.getLocation(2)).hasToString("c");
+		assertThat(bound.getLocation(2).getOrigin()).hasToString(expectedLocation);
+	}
+
 	@Test
 	void bindToValueObjectFromIndexedPropertiesSetsOrigin() {
 		MapConfigurationPropertySource source = new MapConfigurationPropertySource();