Avoid "NullAway.Init" suppression in favor of explicit field handling

Closes gh-36961

spring-web/src/main/java/org/springframework/web/multipart/support/AbstractMultipartHttpServletRequest.java

@@ -44,8 +44,7 @@ import org.springframework.web.multipart.MultipartHttpServletRequest;
 public abstract class AbstractMultipartHttpServletRequest extends HttpServletRequestWrapper
 		implements MultipartHttpServletRequest {
 
-	@SuppressWarnings("NullAway.Init")
-	private MultiValueMap<String, MultipartFile> multipartFiles;
+	private @Nullable MultiValueMap<String, MultipartFile> multipartFiles;
 
 
 	/**
@@ -140,7 +139,7 @@ public abstract class AbstractMultipartHttpServletRequest extends HttpServletReq
 		if (this.multipartFiles == null) {
 			initializeMultipart();
 		}
-		return this.multipartFiles;
+		return (this.multipartFiles != null ? this.multipartFiles : new LinkedMultiValueMap<>(Collections.emptyMap()));
 	}
 
 	/**

spring-web/src/main/java/org/springframework/web/multipart/support/DefaultMultipartHttpServletRequest.java

@@ -45,11 +45,9 @@ public class DefaultMultipartHttpServletRequest extends AbstractMultipartHttpSer
 
 	private static final String CONTENT_TYPE = "Content-Type";
 
-	@SuppressWarnings("NullAway.Init")
-	private Map<String, String[]> multipartParameters;
+	private @Nullable Map<String, String[]> multipartParameters;
 
-	@SuppressWarnings("NullAway.Init")
-	private Map<String, String> multipartParameterContentTypes;
+	private @Nullable Map<String, String> multipartParameterContentTypes;
 
 
 	/**
@@ -170,7 +168,7 @@ public class DefaultMultipartHttpServletRequest extends AbstractMultipartHttpSer
 		if (this.multipartParameters == null) {
 			initializeMultipart();
 		}
-		return this.multipartParameters;
+		return (this.multipartParameters != null ? this.multipartParameters : Collections.emptyMap());
 	}
 
 	/**
@@ -190,7 +188,8 @@ public class DefaultMultipartHttpServletRequest extends AbstractMultipartHttpSer
 		if (this.multipartParameterContentTypes == null) {
 			initializeMultipart();
 		}
-		return this.multipartParameterContentTypes;
+		return (this.multipartParameterContentTypes != null ? this.multipartParameterContentTypes :
+				Collections.emptyMap());
 	}
 
 }

spring-web/src/main/java/org/springframework/web/multipart/support/StandardMultipartHttpServletRequest.java

@@ -58,8 +58,7 @@ import org.springframework.web.multipart.MultipartFile;
  */
 public class StandardMultipartHttpServletRequest extends AbstractMultipartHttpServletRequest {
 
-	@SuppressWarnings("NullAway.Init")
-	private Set<String> multipartParameterNames;
+	private @Nullable Set<String> multipartParameterNames;
 
 
 	/**
@@ -144,7 +143,7 @@ public class StandardMultipartHttpServletRequest extends AbstractMultipartHttpSe
 		if (this.multipartParameterNames == null) {
 			initializeMultipart();
 		}
-		if (this.multipartParameterNames.isEmpty()) {
+		if (CollectionUtils.isEmpty(this.multipartParameterNames)) {
 			return super.getParameterNames();
 		}
 
@@ -164,7 +163,7 @@ public class StandardMultipartHttpServletRequest extends AbstractMultipartHttpSe
 		if (this.multipartParameterNames == null) {
 			initializeMultipart();
 		}
-		if (this.multipartParameterNames.isEmpty()) {
+		if (CollectionUtils.isEmpty(this.multipartParameterNames)) {
 			return super.getParameterMap();
 		}
 

spring-web/src/main/java/org/springframework/web/server/adapter/HttpWebHandlerAdapter.java

@@ -86,8 +86,7 @@ public class HttpWebHandlerAdapter extends WebHandlerDecorator implements HttpHa
 
 	private WebSessionManager sessionManager = new DefaultWebSessionManager();
 
-	@SuppressWarnings("NullAway.Init")
-	private ServerCodecConfigurer codecConfigurer;
+	private @Nullable ServerCodecConfigurer codecConfigurer;
 
 	private LocaleContextResolver localeContextResolver = new AcceptHeaderLocaleContextResolver();
 
@@ -153,10 +152,12 @@ public class HttpWebHandlerAdapter extends WebHandlerDecorator implements HttpHa
 	 * Return the configured {@link ServerCodecConfigurer}.
 	 */
 	public ServerCodecConfigurer getCodecConfigurer() {
-		if (this.codecConfigurer == null) {
-			setCodecConfigurer(ServerCodecConfigurer.create());
+		ServerCodecConfigurer codecConfigurer = this.codecConfigurer;
+		if (codecConfigurer == null) {
+			codecConfigurer = ServerCodecConfigurer.create();
+			setCodecConfigurer(codecConfigurer);
 		}
-		return this.codecConfigurer;
+		return codecConfigurer;
 	}
 
 	/**