Fix NPE in ResponseBodyEmitterReturnValueHandler

The possibility of NPE was introduced in the previous commit:
971ccab038

Issue: SPR-14046

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/ResponseBodyEmitterReturnValueHandler.java

@@ -81,9 +81,11 @@ public class ResponseBodyEmitterReturnValueHandler implements AsyncHandlerMethod
 	}
 
 	private ResponseBodyEmitterAdapter getAdapterFor(Class<?> type) {
-		for (Class<?> adapteeType : getAdapterMap().keySet()) {
-			if (adapteeType.isAssignableFrom(type)) {
-				return getAdapterMap().get(adapteeType);
+		if (type != null) {
+			for (Class<?> adapteeType : getAdapterMap().keySet()) {
+				if (adapteeType.isAssignableFrom(type)) {
+					return getAdapterMap().get(adapteeType);
+				}
 			}
 		}
 		return null;

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ResponseBodyEmitterReturnValueHandlerTests.java

@@ -81,6 +81,7 @@ public class ResponseBodyEmitterReturnValueHandlerTests {
 		assertTrue(this.handler.supportsReturnType(returnType("handleResponseEntity")));
 		assertFalse(this.handler.supportsReturnType(returnType("handleResponseEntityString")));
 		assertFalse(this.handler.supportsReturnType(returnType("handleResponseEntityParameterized")));
+		assertFalse(this.handler.supportsReturnType(returnType("handleRawResponseEntity")));
 	}
 
 	@Test
@@ -229,6 +230,10 @@ public class ResponseBodyEmitterReturnValueHandlerTests {
 			return null;
 		}
 
+		private ResponseEntity handleRawResponseEntity() {
+			return null;
+		}
+
 	}
 
 	private static class SimpleBean {