Add Nullability to spring-security-data

Closes gh-17789

Author: rwinch

data/spring-security-data.gradle

@@ -1,3 +1,7 @@
+plugins {
+	id 'security-nullability'
+}
+
 apply plugin: 'io.spring.convention.spring-module'
 
 dependencies {

data/src/main/java/org/springframework/security/data/repository/query/SecurityEvaluationContextExtension.java

@@ -29,6 +29,8 @@
 import org.springframework.security.core.context.SecurityContextHolder;
 import org.springframework.security.core.context.SecurityContextHolderStrategy;
 import org.springframework.util.Assert;
+import org.jspecify.annotations.Nullable;
+import org.jspecify.annotations.NullUnmarked;
 
 /**
  * <p>
@@ -93,7 +95,7 @@ public class SecurityEvaluationContextExtension implements EvaluationContextExte
 	private SecurityContextHolderStrategy securityContextHolderStrategy = SecurityContextHolder
 		.getContextHolderStrategy();
 
-	private Authentication authentication;
+	private @Nullable Authentication authentication;
 
 	private AuthenticationTrustResolver trustResolver = new AuthenticationTrustResolverImpl();
 
@@ -146,7 +148,7 @@ public void setSecurityContextHolderStrategy(SecurityContextHolderStrategy secur
 		this.securityContextHolderStrategy = securityContextHolderStrategy;
 	}
 
-	private Authentication getAuthentication() {
+	private @Nullable Authentication getAuthentication() {
 		if (this.authentication != null) {
 			return this.authentication;
 		}