Perform NullAway build-time checks in more modules

This commit enables null-safety build-time checks in
all remaining modules except spring-test.

See gh-32475

spring-core/src/main/java/org/springframework/aot/hint/BindingReflectionHintsRegistrar.java

@@ -63,6 +63,7 @@ public class BindingReflectionHintsRegistrar {
 	 * @param hints the hints instance to use
 	 * @param types the types to register
 	 */
+	@SuppressWarnings("NullAway")
 	public void registerReflectionHints(ReflectionHints hints, @Nullable Type... types) {
 		Set<Type> seen = new HashSet<>();
 		for (Type type : types) {

spring-core/src/main/java/org/springframework/core/CoroutinesUtils.java

@@ -108,7 +108,7 @@ public abstract class CoroutinesUtils {
 	 * @throws IllegalArgumentException if {@code method} is not a suspending function
 	 * @since 6.0
 	 */
-	@SuppressWarnings({"deprecation", "DataFlowIssue"})
+	@SuppressWarnings({"deprecation", "DataFlowIssue", "NullAway"})
 	public static Publisher<?> invokeSuspendingFunction(
 			CoroutineContext context, Method method, @Nullable Object target, @Nullable Object... args) {
 

spring-core/src/main/java/org/springframework/util/PlaceholderParser.java

@@ -322,6 +322,7 @@ final class PlaceholderParser {
 		}
 
 		@Override
+		@Nullable
 		public String resolvePlaceholder(String placeholderName) {
 			String value = this.resolver.resolvePlaceholder(placeholderName);
 			if (value != null && logger.isTraceEnabled()) {
@@ -358,6 +359,7 @@ final class PlaceholderParser {
 		}
 
 		public void removePlaceholder(String placeholder) {
+			Assert.state(this.visitedPlaceholders != null, "Visited placeholders must not be null");
 			this.visitedPlaceholders.remove(placeholder);
 		}
 

spring-core/src/main/java/org/springframework/util/StreamUtils.java

@@ -25,6 +25,7 @@ import java.io.InputStreamReader;
 import java.io.OutputStream;
 import java.nio.charset.Charset;
 
+import org.springframework.lang.Contract;
 import org.springframework.lang.Nullable;
 
 /**
@@ -201,6 +202,7 @@ public abstract class StreamUtils {
 	 * @throws IOException in case of I/O errors
 	 * @since 4.3
 	 */
+	@Contract("null -> fail")
 	public static int drain(@Nullable InputStream in) throws IOException {
 		Assert.notNull(in, "No InputStream specified");
 		return (int) in.transferTo(OutputStream.nullOutputStream());