Fix some NullAway wildcard warnings

Signed-off-by: Manu Sridharan <msridhar@gmail.com>

Author: msridhar

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/CachingJupiterConfiguration.java

@@ -33,6 +33,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.ClassOrderer;
 import org.junit.jupiter.api.Constants;
 import org.junit.jupiter.api.DisplayNameGenerator;
@@ -73,7 +74,8 @@ public Optional<String> getRawConfigurationParameter(String key) {
 	}
 
 	@Override
-	public <T> Optional<T> getRawConfigurationParameter(String key, Function<? super String, ? extends T> transformer) {
+	public <T> Optional<T> getRawConfigurationParameter(String key,
+			Function<? super String, ? extends @Nullable T> transformer) {
 		return delegate.getRawConfigurationParameter(key, transformer);
 	}
 

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/DefaultJupiterConfiguration.java

@@ -42,6 +42,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.ClassOrderer;
 import org.junit.jupiter.api.DisplayNameGenerator;
 import org.junit.jupiter.api.MethodOrderer;
@@ -160,7 +161,8 @@ public Optional<String> getRawConfigurationParameter(String key) {
 	}
 
 	@Override
-	public <T> Optional<T> getRawConfigurationParameter(String key, Function<? super String, ? extends T> transformer) {
+	public <T> Optional<T> getRawConfigurationParameter(String key,
+			Function<? super String, ? extends @Nullable T> transformer) {
 		return configurationParameters.get(key, transformer);
 	}
 

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/config/JupiterConfiguration.java

@@ -18,6 +18,7 @@
 import java.util.function.Supplier;
 
 import org.apiguardian.api.API;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.ClassOrderer;
 import org.junit.jupiter.api.DisplayNameGenerator;
 import org.junit.jupiter.api.MethodOrderer;
@@ -41,7 +42,8 @@ public interface JupiterConfiguration {
 
 	Optional<String> getRawConfigurationParameter(String key);
 
-	<T> Optional<T> getRawConfigurationParameter(String key, Function<? super String, ? extends T> transformer);
+	<T> Optional<T> getRawConfigurationParameter(String key,
+			Function<? super String, ? extends @Nullable T> transformer);
 
 	boolean isParallelExecutionEnabled();