Add missing @nullable annotations in AbstractResourceResolver subclasses

See gh-30601
Closes gh-30893

Author: izeye

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/CachingResourceResolver.java

@@ -106,6 +106,7 @@ public List<String> getContentCodings() {
 
 
 	@Override
+	@Nullable
 	protected Resource resolveResourceInternal(@Nullable HttpServletRequest request, String requestPath,
 			List<? extends Resource> locations, ResourceResolverChain chain) {
 
@@ -154,6 +155,7 @@ private String getContentCodingKey(HttpServletRequest request) {
 	}
 
 	@Override
+	@Nullable
 	protected String resolveUrlPathInternal(String resourceUrlPath,
 			List<? extends Resource> locations, ResourceResolverChain chain) {
 

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/EncodedResourceResolver.java

@@ -129,6 +129,7 @@ public void registerExtension(String coding, String extension) {
 
 
 	@Override
+	@Nullable
 	protected Resource resolveResourceInternal(@Nullable HttpServletRequest request, String requestPath,
 			List<? extends Resource> locations, ResourceResolverChain chain) {
 
@@ -177,6 +178,7 @@ private String getExtension(String coding) {
 	}
 
 	@Override
+	@Nullable
 	protected String resolveUrlPathInternal(String resourceUrlPath,
 			List<? extends Resource> locations, ResourceResolverChain chain) {
 

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/VersionResourceResolver.java

@@ -157,6 +157,7 @@ public VersionResourceResolver addVersionStrategy(VersionStrategy strategy, Stri
 
 
 	@Override
+	@Nullable
 	protected Resource resolveResourceInternal(@Nullable HttpServletRequest request, String requestPath,
 			List<? extends Resource> locations, ResourceResolverChain chain) {
 
@@ -195,6 +196,7 @@ protected Resource resolveResourceInternal(@Nullable HttpServletRequest request,
 	}
 
 	@Override
+	@Nullable
 	protected String resolveUrlPathInternal(String resourceUrlPath,
 			List<? extends Resource> locations, ResourceResolverChain chain) {
 

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/WebJarsResourceResolver.java

@@ -74,6 +74,7 @@ public WebJarsResourceResolver(WebJarAssetLocator webJarAssetLocator) {
 
 
 	@Override
+	@Nullable
 	protected Resource resolveResourceInternal(@Nullable HttpServletRequest request, String requestPath,
 			List<? extends Resource> locations, ResourceResolverChain chain) {
 
@@ -88,6 +89,7 @@ protected Resource resolveResourceInternal(@Nullable HttpServletRequest request,
 	}
 
 	@Override
+	@Nullable
 	protected String resolveUrlPathInternal(String resourceUrlPath,
 			List<? extends Resource> locations, ResourceResolverChain chain) {