Restore accidentally deleted line

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/main/java/org/springframework/boot/buildpack/platform/build/BuildRequest.java

@@ -235,6 +235,7 @@ public class BuildRequest {
 	 * @return a new build request instance
 	 */
 	public static BuildRequest forJarFile(File jarFile) {
+		assertJarFile(jarFile);
 		return forJarFile(ImageReference.forJarFile(jarFile).inTaggedForm(), jarFile);
 	}