[Cosmos] Fix ClassCastException when building CosmosException from an empty error response body

sdk/cosmos/azure-cosmos-tests/src/test/java/com/azure/cosmos/implementation/JsonSerializableTest.java

@@ -11,6 +11,8 @@
 import org.testng.annotations.Test;
 
 import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.List;
 
@@ -34,4 +36,22 @@ public void instantiateWithObjectNodeAndType() throws IOException {
             assertThat(jsonSerializable).isInstanceOf(klass);
         }
     }
+
+    @Test(groups = {"unit"})
+    public void instantiateFromNonObjectJsonReturnsEmptyObject() {
+        for (String body : Arrays.asList("", "   ", "null", "[]", "123")) {
+            JsonSerializable jsonSerializable = new JsonSerializable(body);
+            assertThat(jsonSerializable.propertyBag).isNotNull();
+            assertThat(jsonSerializable.propertyBag.isEmpty()).isTrue();
+        }
+    }
+
+    @Test(groups = {"unit"})
+    public void instantiateFromNonObjectJsonBytesReturnsEmptyObject() {
+        for (String body : Arrays.asList("", "null", "[]", "123")) {
+            byte[] bytes = body.getBytes(StandardCharsets.UTF_8);
+            assertThat(new JsonSerializable(bytes).propertyBag.isEmpty()).isTrue();
+            assertThat(new JsonSerializable(ByteBuffer.wrap(bytes)).propertyBag.isEmpty()).isTrue();
+        }
+    }
 }

sdk/cosmos/azure-cosmos/CHANGELOG.md

@@ -12,6 +12,7 @@
 #### Other Changes
 * Replaced per-client `Schedulers.newSingle()` schedulers in `GlobalEndpointManager` and `GlobalPartitionEndpointManagerForPerPartitionCircuitBreaker` with shared `BoundedElastic` schedulers in `CosmosSchedulers` to prevent thread count from scaling linearly with client/tenant count. - See [PR 49062](https://github.com/Azure/azure-sdk-for-java/pull/49062)
 * Fixed a sporadic `NullPointerException` in `JsonSerializable.getWithMapping` triggered by concurrent first-time calls to `DatabaseAccount.getConsistencyPolicy()` and its sibling lazy getters (`getReplicationPolicy`, `getSystemReplicationPolicy`, `getQueryEngineConfiguration`). The fix makes `JsonSerializable.propertyBag` `final`, closing an unsafe-publication race in the lazy-initialisation pattern. - See [Issue 49256](https://github.com/Azure/azure-sdk-for-java/issues/49256) and [PR #49258](https://github.com/Azure/azure-sdk-for-java/pull/49258)
+* Fixed a `ClassCastException` (`MissingNode cannot be cast to ObjectNode`) thrown by `JsonSerializable` when parsing an empty, blank or non-object payload. Non-object payloads are now treated as an empty object across the `String`, `byte[]` and `ByteBuffer` parsing paths. - See [Issue 49322](https://github.com/Azure/azure-sdk-for-java/issues/49322)
 
 ### 4.80.0 (2026-05-01)
 

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/JsonSerializable.java

@@ -606,7 +606,11 @@ public Object getObjectByPath(List<String> propertyNames) {
 
     private ObjectNode fromJson(byte[] bytes) {
         try {
-            return (ObjectNode) OBJECT_MAPPER.readTree(bytes);
+            JsonNode jsonNode = OBJECT_MAPPER.readTree(bytes);
+            if (jsonNode instanceof ObjectNode) {
+                return (ObjectNode) jsonNode;
+            }
+            return OBJECT_MAPPER.createObjectNode();
         } catch (IOException e) {
             throw new IllegalArgumentException(
                 String.format("Unable to parse JSON %s", Arrays.toString(bytes)), e);
@@ -615,7 +619,11 @@ private ObjectNode fromJson(byte[] bytes) {
 
     private ObjectNode fromJson(String json, ObjectMapper objectMapper) {
         try {
-            return (ObjectNode) objectMapper.readTree(json);
+            JsonNode jsonNode = objectMapper.readTree(json);
+            if (jsonNode instanceof ObjectNode) {
+                return (ObjectNode) jsonNode;
+            }
+            return objectMapper.createObjectNode();
         } catch (IOException e) {
             throw new IllegalArgumentException(
                 String.format("Unable to parse JSON %s", json), e);
@@ -624,7 +632,11 @@ private ObjectNode fromJson(String json, ObjectMapper objectMapper) {
 
     private ObjectNode fromJson(ByteBuffer json) {
         try {
-            return (ObjectNode) OBJECT_MAPPER.readTree(new ByteBufferBackedInputStream(json));
+            JsonNode jsonNode = OBJECT_MAPPER.readTree(new ByteBufferBackedInputStream(json));
+            if (jsonNode instanceof ObjectNode) {
+                return (ObjectNode) jsonNode;
+            }
+            return OBJECT_MAPPER.createObjectNode();
         } catch (IOException e) {
             throw new IllegalArgumentException("Unable to parse JSON from ByteBuffer", e);
         }