Add nullability annotations to tests in module/spring-boot-gson

See gh-47263

module/spring-boot-gson/build.gradle

@@ -36,3 +36,7 @@ dependencies {
 
 	testRuntimeOnly("ch.qos.logback:logback-classic")
 }
+
+tasks.named("compileTestJava") {
+	options.nullability.checking = "tests"
+}

module/spring-boot-gson/src/test/java/org/springframework/boot/gson/autoconfigure/Gson210AutoConfigurationTests.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.gson.autoconfigure;
 
 import com.google.gson.Gson;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.autoconfigure.AutoConfigurations;
@@ -52,7 +53,7 @@ class Gson210AutoConfigurationTests {
 		private Long data = 1L;
 
 		@SuppressWarnings("unused")
-		private final String owner = null;
+		private final @Nullable String owner = null;
 
 		public void setData(Long data) {
 			this.data = data;

module/spring-boot-gson/src/test/java/org/springframework/boot/gson/autoconfigure/GsonAutoConfigurationTests.java

@@ -29,6 +29,7 @@ import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.LongSerializationPolicy;
 import com.google.gson.Strictness;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.skyscreamer.jsonassert.JSONAssert;
 
@@ -310,7 +311,7 @@ class GsonAutoConfigurationTests {
 		private Long data = 1L;
 
 		@SuppressWarnings("unused")
-		private final String owner = null;
+		private final @Nullable String owner = null;
 
 		public void setData(Long data) {
 			this.data = data;