Fix overridden methods nullability

Issue: SPR-15869

spring-test/src/main/java/org/springframework/mock/web/MockServletContext.java

@@ -266,6 +266,7 @@ public class MockServletContext implements ServletContext {
 	}
 
 	@Override
+	@Nullable
 	public String getMimeType(String filePath) {
 		String extension = StringUtils.getFilenameExtension(filePath);
 		if (this.mimeTypes.containsKey(extension)) {

spring-test/src/main/java/org/springframework/test/context/cache/DefaultContextCache.java

@@ -118,6 +118,7 @@ public class DefaultContextCache implements ContextCache {
 	 * {@inheritDoc}
 	 */
 	@Override
+	@Nullable
 	public ApplicationContext get(MergedContextConfiguration key) {
 		Assert.notNull(key, "Key must not be null");
 		ApplicationContext context = this.contextMap.get(key);

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

@@ -147,6 +147,7 @@ public class DefaultTestContext implements TestContext {
 		return testMethod;
 	}
 
+	@Override
 	@Nullable
 	public final Throwable getTestException() {
 		return this.testException;
@@ -172,12 +173,14 @@ public class DefaultTestContext implements TestContext {
 	}
 
 	@Override
+	@Nullable
 	public Object getAttribute(String name) {
 		Assert.notNull(name, "Name must not be null");
 		return this.attributes.get(name);
 	}
 
 	@Override
+	@Nullable
 	public Object removeAttribute(String name) {
 		Assert.notNull(name, "Name must not be null");
 		return this.attributes.remove(name);

spring-test/src/main/java/org/springframework/test/context/transaction/TestContextTransactionUtils.java

@@ -251,6 +251,7 @@ public abstract class TestContextTransactionUtils {
 		}
 
 		@Override
+		@Nullable
 		public String getName() {
 			return this.name;
 		}

spring-test/src/main/java/org/springframework/test/context/web/socket/MockServerContainerContextCustomizerFactory.java

@@ -20,6 +20,7 @@ import java.util.List;
 
 import org.springframework.beans.BeanUtils;
 import org.springframework.core.annotation.AnnotatedElementUtils;
+import org.springframework.lang.Nullable;
 import org.springframework.test.context.ContextConfigurationAttributes;
 import org.springframework.test.context.ContextCustomizer;
 import org.springframework.test.context.ContextCustomizerFactory;
@@ -46,6 +47,7 @@ class MockServerContainerContextCustomizerFactory implements ContextCustomizerFa
 
 
 	@Override
+	@Nullable
 	public ContextCustomizer createContextCustomizer(Class<?> testClass,
 			List<ContextConfigurationAttributes> configAttributes) {
 

spring-test/src/main/java/org/springframework/test/web/reactive/server/FluxExchangeResult.java

@@ -21,6 +21,8 @@ import java.time.Duration;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
+import org.springframework.lang.Nullable;
+
 /**
  * {@code ExchangeResult} variant with the response body decoded as
  * {@code Flux<T>} but not yet consumed.
@@ -87,6 +89,7 @@ public class FluxExchangeResult<T> extends ExchangeResult {
 	 * via {@code getResponseBody.ignoreElements()}.
 	 */
 	@Override
+	@Nullable
 	public byte[] getResponseBodyContent() {
 		return this.body.ignoreElements()
 				.timeout(this.timeout, Mono.error(TIMEOUT_ERROR))

spring-test/src/main/java/org/springframework/test/web/servlet/setup/MockMvcConfigurerAdapter.java

@@ -16,6 +16,7 @@
 
 package org.springframework.test.web.servlet.setup;
 
+import org.springframework.lang.Nullable;
 import org.springframework.test.web.servlet.request.RequestPostProcessor;
 import org.springframework.web.context.WebApplicationContext;
 
@@ -32,6 +33,7 @@ public abstract class MockMvcConfigurerAdapter implements MockMvcConfigurer {
 	}
 
 	@Override
+	@Nullable
 	public RequestPostProcessor beforeMockMvcCreated(ConfigurableMockMvcBuilder<?> builder, WebApplicationContext cxt) {
 		return null;
 	}

spring-test/src/main/java/org/springframework/test/web/servlet/setup/StandaloneMockMvcBuilder.java

@@ -539,6 +539,7 @@ public class StandaloneMockMvcBuilder extends AbstractMockMvcBuilder<StandaloneM
 		}
 
 		@Override
+		@Nullable
 		public View resolveViewName(String viewName, Locale locale) throws Exception {
 			return this.view;
 		}

spring-test/src/main/java/org/springframework/test/web/servlet/setup/StubWebApplicationContext.java

@@ -275,6 +275,7 @@ class StubWebApplicationContext implements WebApplicationContext {
 	}
 
 	@Override
+	@Nullable
 	public <A extends Annotation> A findAnnotationOnBean(String beanName, Class<A> annotationType)
 			throws NoSuchBeanDefinitionException{
 
@@ -322,6 +323,7 @@ class StubWebApplicationContext implements WebApplicationContext {
 	//---------------------------------------------------------------------
 
 	@Override
+	@Nullable
 	public ClassLoader getClassLoader() {
 		return ClassUtils.getDefaultClassLoader();
 	}
@@ -399,11 +401,13 @@ class StubWebApplicationContext implements WebApplicationContext {
 		}
 
 		@Override
+		@Nullable
 		public Object resolveDependency(DependencyDescriptor descriptor, @Nullable String requestingBeanName) {
 			throw new UnsupportedOperationException("Dependency resolution not supported");
 		}
 
 		@Override
+		@Nullable
 		public Object resolveDependency(DependencyDescriptor descriptor, @Nullable String requestingBeanName,
 				@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) {
 			throw new UnsupportedOperationException("Dependency resolution not supported");