@@ -36,6 +36,7 @@
 import org.apache.hc.core5.http.Header;
 import org.apache.hc.core5.http.HttpException;
 import org.apache.hc.core5.http.nio.AsyncDataConsumer;
+import org.apache.hc.core5.util.Args;
 import org.apache.hc.core5.http.nio.CapacityChannel;
 
 /**
@@ -65,7 +66,7 @@ public final class InflatingAsyncDataConsumer implements AsyncDataConsumer {
 
     public InflatingAsyncDataConsumer(
             final AsyncDataConsumer downstream, final Boolean nowrapHint) {
-        this.downstream = downstream;
+        this.downstream = Args.notNull(downstream, "Downstream data consumer");
         this.nowrapHint = nowrapHint;
         this.inflater = new Inflater(nowrapHint == null || nowrapHint);
     }
 
@@ -35,6 +35,7 @@
 import org.apache.hc.core5.http.Header;
 import org.apache.hc.core5.http.HttpException;
 import org.apache.hc.core5.http.nio.AsyncDataConsumer;
+import org.apache.hc.core5.util.Args;
 import org.apache.hc.core5.http.nio.CapacityChannel;
 import org.apache.hc.core5.util.Asserts;
 
@@ -70,7 +71,7 @@ public final class InflatingBrotliDataConsumer implements AsyncDataConsumer {
 
 
     public InflatingBrotliDataConsumer(final AsyncDataConsumer downstream) {
-        this.downstream = downstream;
+        this.downstream = Args.notNull(downstream, "Downstream data consumer");
         try {
             this.decoder = new DecoderJNI.Wrapper(8 * 1024);
         } catch (final IOException e) {
 
@@ -39,6 +39,7 @@
 import org.apache.hc.core5.http.Header;
 import org.apache.hc.core5.http.HttpException;
 import org.apache.hc.core5.http.nio.AsyncDataConsumer;
+import org.apache.hc.core5.util.Args;
 import org.apache.hc.core5.http.nio.CapacityChannel;
 
 /**
@@ -65,7 +66,7 @@ public final class InflatingGzipDataConsumer implements AsyncDataConsumer {
     private final AtomicBoolean closed = new AtomicBoolean(false);
 
     public InflatingGzipDataConsumer(final AsyncDataConsumer downstream) {
-        this.downstream = downstream;
+        this.downstream = Args.notNull(downstream, "Downstream data consumer");
     }
 
     @Override
 
@@ -36,6 +36,7 @@
 import org.apache.hc.core5.http.Header;
 import org.apache.hc.core5.http.HttpException;
 import org.apache.hc.core5.http.nio.AsyncDataConsumer;
+import org.apache.hc.core5.util.Args;
 import org.apache.hc.core5.http.nio.CapacityChannel;
 
 /**
@@ -73,7 +74,7 @@ public final class InflatingZstdDataConsumer implements AsyncDataConsumer {
     private final AtomicBoolean closed = new AtomicBoolean(false);
 
     public InflatingZstdDataConsumer(final AsyncDataConsumer downstream) {
-        this.downstream = downstream;
+        this.downstream = Args.notNull(downstream, "Downstream data consumer");
         inDirect.limit(0);
         outDirect.limit(0);
     }
 
@@ -152,6 +152,9 @@ public AsyncDataConsumer handleResponse(final HttpResponse rsp,
                 ContentCodingSupport.validate(codecs, maxCodecListLen);
                 if (!codecs.isEmpty()) {
                     AsyncDataConsumer downstream = cb.handleResponse(rsp, wrapEntityDetails(details));
+                    if (downstream == null) {
+                        return null;
+                    }
                     for (int i = codecs.size() - 1; i >= 0; i--) {
                         final String codec = codecs.get(i);
                         final UnaryOperator<AsyncDataConsumer> op = decoders.lookup(codec);
 
@@ -0,0 +1,39 @@
+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+package org.apache.hc.client5.http.async.methods;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+class TestInflatingGzipDataConsumerNullDownstream {
+
+    @Test
+    void gzipConsumerRejectsNullDownstreamAtConstruction() {
+        assertThrows(NullPointerException.class, () -> new InflatingGzipDataConsumer(null));
+    }
+
+}
@@ -29,6 +29,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -130,7 +131,8 @@ void testDeflateConsumerInserted() throws Exception {
         when(details.getContentEncoding()).thenReturn("deflate");
 
         final AsyncDataConsumer downstream = new StringAsyncEntityConsumer();
-        when(originalCb.handleResponse(same(rsp), same(details))).thenReturn(downstream);
+        // the exec passes a wrapped EntityDetails downstream, so match any (not same(details))
+        when(originalCb.handleResponse(same(rsp), any(EntityDetails.class))).thenReturn(downstream);
 
         final AsyncDataConsumer wrapped = cb.handleResponse(rsp, details);
 
@@ -172,6 +174,10 @@ public AsyncDataConsumer apply(final AsyncDataConsumer d) {
         final HttpResponse rsp = new BasicHttpResponse(200, "OK");
         final EntityDetails details = mock(EntityDetails.class);
         when(details.getContentEncoding()).thenReturn("whatever");
+        // a real (non-null) downstream so the exec proceeds to decoder selection and rejects the
+        // unknown coding; a null downstream would legitimately be discarded without decoding
+        when(originalCb.handleResponse(same(rsp), any(EntityDetails.class)))
+                .thenReturn(new StringAsyncEntityConsumer());
 
         assertThrows(HttpException.class, () -> cb.handleResponse(rsp, details));
     }
@@ -197,7 +203,7 @@ void testContentEncodingExceedsCodecListLenMax() throws Exception {
         when(details1.getContentEncoding()).thenReturn("gzip,gzip,gzip,gzip,gzip");
 
         final AsyncDataConsumer downstream1 = new StringAsyncEntityConsumer();
-        when(originalCb.handleResponse(same(rsp1), same(details1))).thenReturn(downstream1);
+        when(originalCb.handleResponse(same(rsp1), any(EntityDetails.class))).thenReturn(downstream1);
 
         final AsyncDataConsumer wrapped = cb.handleResponse(rsp1, details1);
 
@@ -214,4 +220,20 @@ void testContentEncodingExceedsCodecListLenMax() throws Exception {
         assertEquals("Codec list exceeds maximum of 5 elements", exception.getMessage());
     }
 
+    @Test
+    void propagatesNullDiscardOnEncodedResponse() throws Exception {
+        final HttpRequest request = new BasicHttpRequest(Method.GET, "/");
+        final AsyncExecCallback cb = executeAndCapture(request);
+
+        final HttpResponse rsp = new BasicHttpResponse(302, "Found");
+        final EntityDetails details = mock(EntityDetails.class);
+        when(details.getContentEncoding()).thenReturn("gzip");
+
+        // an upstream exec (e.g. AsyncRedirectExec on a redirect) discards the body by returning null
+        when(originalCb.handleResponse(same(rsp), any(EntityDetails.class))).thenReturn(null);
+
+        // the null-discard signal must be propagated, not wrapped in a decoder (HTTPCLIENT-2426)
+        assertNull(cb.handleResponse(rsp, details));
+    }
+
 }