Consistently declare @⁠Nullable on parameter in equals() implementations

Closes gh-36075

Signed-off-by: 木葉 Scarlet <93977077+mukjepscarlet@users.noreply.github.com>

spring-web/src/main/java/org/springframework/http/ETag.java

@@ -21,6 +21,7 @@ import java.util.List;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.util.StringUtils;
 
@@ -68,7 +69,7 @@ public record ETag(String tag, boolean weak) {
 	}
 
 	@Override
-	public boolean equals(Object other) {
+	public boolean equals(@Nullable Object other) {
 		return (this == other ||
 				(other instanceof ETag oet && this.tag.equals(oet.tag) && this.weak == oet.weak));
 	}

spring-web/src/main/java/org/springframework/http/HttpHeaders.java

@@ -2331,7 +2331,7 @@ public class HttpHeaders implements Serializable {
 			}
 
 			@Override
-			public boolean equals(Object o) {
+			public boolean equals(@Nullable Object o) {
 				if (this == o) {
 					return true;
 				}

spring-web/src/main/java/org/springframework/web/accept/SemanticApiVersionParser.java

@@ -19,6 +19,8 @@ package org.springframework.web.accept;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.util.Assert;
 
 /**
@@ -106,7 +108,7 @@ public class SemanticApiVersionParser implements ApiVersionParser<SemanticApiVer
 		}
 
 		@Override
-		public boolean equals(Object other) {
+		public boolean equals(@Nullable Object other) {
 			return (this == other || (other instanceof Version otherVersion &&
 					this.major == otherVersion.major &&
 					this.minor == otherVersion.minor &&

spring-web/src/main/java/org/springframework/web/service/invoker/HttpServiceMethod.java

@@ -364,7 +364,7 @@ final class HttpServiceMethod {
 			}
 
 			@Override
-			public boolean equals(Object obj) {
+			public boolean equals(@Nullable Object obj) {
 				return (obj instanceof AnnotationDescriptor that && this.httpExchange.equals(that.httpExchange));
 			}
 

spring-web/src/main/java/org/springframework/web/util/WhatWgUrlParser.java

@@ -2019,7 +2019,7 @@ final class WhatWgUrlParser {
 		}
 
 		@Override
-		public boolean equals(Object obj) {
+		public boolean equals(@Nullable Object obj) {
 			if (obj == this) {
 				return true;
 			}
@@ -2160,7 +2160,7 @@ final class WhatWgUrlParser {
 		}
 
 		@Override
-		public boolean equals(Object o) {
+		public boolean equals(@Nullable Object o) {
 			if (o == this) {
 				return true;
 			}
@@ -2207,7 +2207,7 @@ final class WhatWgUrlParser {
 		}
 
 		@Override
-		public boolean equals(Object obj) {
+		public boolean equals(@Nullable Object obj) {
 			if (obj == this) {
 				return true;
 			}
@@ -2271,7 +2271,7 @@ final class WhatWgUrlParser {
 		}
 
 		@Override
-		public boolean equals(Object obj) {
+		public boolean equals(@Nullable Object obj) {
 			if (obj == this) {
 				return true;
 			}
@@ -2304,7 +2304,7 @@ final class WhatWgUrlParser {
 		}
 
 		@Override
-		public boolean equals(Object obj) {
+		public boolean equals(@Nullable Object obj) {
 			return obj == this || obj != null && getClass() == obj.getClass();
 		}
 
@@ -2503,7 +2503,7 @@ final class WhatWgUrlParser {
 
 
 		@Override
-		public boolean equals(Object o) {
+		public boolean equals(@Nullable Object o) {
 			if (o == this) {
 				return true;
 			}
@@ -2812,7 +2812,7 @@ final class WhatWgUrlParser {
 		}
 
 		@Override
-		public boolean equals(Object obj) {
+		public boolean equals(@Nullable Object obj) {
 			if (obj == this) {
 				return true;
 			}
@@ -2978,7 +2978,7 @@ final class WhatWgUrlParser {
 		}
 
 		@Override
-		public boolean equals(Object o) {
+		public boolean equals(@Nullable Object o) {
 			if (o == this) {
 				return true;
 			}
@@ -3073,7 +3073,7 @@ final class WhatWgUrlParser {
 		}
 
 		@Override
-		public boolean equals(Object o) {
+		public boolean equals(@Nullable Object o) {
 			if (o == this) {
 				return true;
 			}