Nullability refinements and related polishing

See gh-32475

spring-test/src/main/java/org/springframework/test/context/aot/GeneratedMapUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -42,14 +42,14 @@ final class GeneratedMapUtils {
 	 * @param methodName the name of the static method to invoke
 	 * @return an unmodifiable map retrieved from a static method
 	 */
-	@SuppressWarnings({ "rawtypes", "unchecked" })
+	@SuppressWarnings({"rawtypes", "unchecked"})
 	static Map loadMap(String className, String methodName) {
 		try {
 			Class<?> clazz = ClassUtils.forName(className, null);
 			Method method = ReflectionUtils.findMethod(clazz, methodName);
 			Assert.state(method != null, () -> "No %s() method found in %s".formatted(methodName, className));
 			Map map = (Map) ReflectionUtils.invokeMethod(method, null);
-			return Collections.unmodifiableMap(map);
+			return (map != null ? Collections.unmodifiableMap(map) : Collections.emptyMap());
 		}
 		catch (IllegalStateException ex) {
 			throw ex;

spring-test/src/main/java/org/springframework/test/context/aot/TestContextGenerationContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -20,6 +20,7 @@ import org.springframework.aot.generate.ClassNameGenerator;
 import org.springframework.aot.generate.DefaultGenerationContext;
 import org.springframework.aot.generate.GeneratedFiles;
 import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.lang.Nullable;
 
 /**
  * Extension of {@link DefaultGenerationContext} with a custom implementation of
@@ -30,6 +31,7 @@ import org.springframework.aot.hint.RuntimeHints;
  */
 class TestContextGenerationContext extends DefaultGenerationContext {
 
+	@Nullable
 	private final String featureName;
 
 
@@ -41,8 +43,9 @@ class TestContextGenerationContext extends DefaultGenerationContext {
 	 * @param generatedFiles the generated files
 	 * @param runtimeHints the runtime hints
 	 */
-	TestContextGenerationContext(ClassNameGenerator classNameGenerator, GeneratedFiles generatedFiles,
-			RuntimeHints runtimeHints) {
+	TestContextGenerationContext(
+			ClassNameGenerator classNameGenerator, GeneratedFiles generatedFiles, RuntimeHints runtimeHints) {
+
 		super(classNameGenerator, generatedFiles, runtimeHints);
 		this.featureName = null;
 	}

spring-test/src/main/java/org/springframework/test/context/observation/MicrometerObservationRegistryTestExecutionListener.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -25,6 +25,7 @@ import org.apache.commons.logging.LogFactory;
 
 import org.springframework.context.ApplicationContext;
 import org.springframework.core.Conventions;
+import org.springframework.lang.Nullable;
 import org.springframework.test.context.TestContext;
 import org.springframework.test.context.support.AbstractTestExecutionListener;
 import org.springframework.util.ReflectionUtils;
@@ -67,6 +68,7 @@ class MicrometerObservationRegistryTestExecutionListener extends AbstractTestExe
 	static final String OBSERVATION_THREAD_LOCAL_ACCESSOR_CLASS_NAME =
 			"io.micrometer.observation.contextpropagation.ObservationThreadLocalAccessor";
 
+	@Nullable
 	private static final String ERROR_MESSAGE;
 
 	static {

spring-test/src/main/java/org/springframework/test/context/support/TestPropertySourceAttributes.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -143,7 +143,7 @@ class TestPropertySourceAttributes {
 	}
 
 	private void addPropertiesAndLocations(List<PropertySourceDescriptor> descriptors, String[] properties,
-			Class<?> declaringClass, String encoding, boolean prepend) {
+			Class<?> declaringClass, @Nullable String encoding, boolean prepend) {
 
 		if (hasNoLocations(descriptors) && ObjectUtils.isEmpty(properties)) {
 			String defaultPropertiesFile = detectDefaultPropertiesFile(declaringClass);