Add isEmpty() to HttpMessageConverters

See gh-35793

spring-web/src/main/java/org/springframework/http/converter/DefaultHttpMessageConverters.java

@@ -57,10 +57,17 @@ class DefaultHttpMessageConverters implements HttpMessageConverters {
 
 	private final List<HttpMessageConverter<?>> messageConverters;
 
+
 	DefaultHttpMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
 		this.messageConverters = messageConverters;
 	}
 
+
+	@Override
+	public boolean isEmpty() {
+		return this.messageConverters.isEmpty();
+	}
+
 	@Override
 	public Iterator<HttpMessageConverter<?>> iterator() {
 		return this.messageConverters.iterator();

spring-web/src/main/java/org/springframework/http/converter/HttpMessageConverters.java

@@ -32,6 +32,11 @@ import java.util.function.Consumer;
  */
 public interface HttpMessageConverters extends Iterable<HttpMessageConverter<?>> {
 
+	/**
+	 * Return true if this instance does not contain any message converters.
+	 */
+	boolean isEmpty();
+
 	/**
 	 * Create a builder instance, tailored for HTTP client usage.
 	 * <p>The following HTTP message converters can be detected and registered if available, in order: