wrap null qname deref in xsb group loaders

src/main/java/org/apache/xmlbeans/impl/schema/XsbReader.java

@@ -751,12 +751,11 @@ public SchemaGlobalAttribute finishLoadingAttribute() {
     }
 
     SchemaModelGroup finishLoadingModelGroup() {
-        QName name = readQName();
-        SchemaContainer container = typeSystem.getContainer(name.getNamespaceURI());
-        checkContainerNotNull(container, name);
-        SchemaModelGroupImpl impl = new SchemaModelGroupImpl(container);
-
         try {
+            QName name = readQName();
+            SchemaContainer container = typeSystem.getContainer(name.getNamespaceURI());
+            checkContainerNotNull(container, name);
+            SchemaModelGroupImpl impl = new SchemaModelGroupImpl(container);
             impl.init(name, readString(), readShort() == 1,
                 atLeast(2, 22, 0) ? readString() : null,
                 atLeast(2, 22, 0) ? readString() : null,
@@ -820,12 +819,11 @@ SchemaIdentityConstraint finishLoadingIdentityConstraint() {
     }
 
     SchemaAttributeGroup finishLoadingAttributeGroup() {
-        QName name = readQName();
-        SchemaContainer container = typeSystem.getContainer(name.getNamespaceURI());
-        checkContainerNotNull(container, name);
-        SchemaAttributeGroupImpl impl = new SchemaAttributeGroupImpl(container);
-
         try {
+            QName name = readQName();
+            SchemaContainer container = typeSystem.getContainer(name.getNamespaceURI());
+            checkContainerNotNull(container, name);
+            SchemaAttributeGroupImpl impl = new SchemaAttributeGroupImpl(container);
             impl.init(name, readString(), readShort() == 1,
                 atLeast(2, 22, 0) ? readString() : null,
                 atLeast(2, 15, 0) && readShort() == 1,

src/test/java/org/apache/xmlbeans/impl/schema/XsbReaderGroupQNameTest.java

@@ -0,0 +1,65 @@
+/*   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.
+ */
+
+package org.apache.xmlbeans.impl.schema;
+
+import org.apache.xmlbeans.SchemaTypeLoaderException;
+import org.apache.xmlbeans.impl.util.LongUTFDataInputStream;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.DataOutputStream;
+import java.lang.reflect.Field;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class XsbReaderGroupQNameTest {
+
+    // Builds an XsbReader whose first readQName() returns null, exactly as a
+    // crafted .xsb would supply it: writeQName encodes a null name as two null
+    // string codes (code 0), and stringForCode(0) returns null so readQName
+    // hands back null for a zero local-part code.
+    private static XsbReader readerForNullQName() throws Exception {
+        XsbReader reader = new XsbReader(new SchemaTypeSystemImpl("test"), "h");
+
+        ByteArrayOutputStream bos = new ByteArrayOutputStream();
+        DataOutputStream dos = new DataOutputStream(bos);
+        dos.writeShort(0); // namespace string code -> null
+        dos.writeShort(0); // localname string code -> null -> readQName returns null
+        dos.flush();
+
+        Field inputF = XsbReader.class.getDeclaredField("_input");
+        inputF.setAccessible(true);
+        inputF.set(reader, new LongUTFDataInputStream(new ByteArrayInputStream(bos.toByteArray())));
+
+        return reader;
+    }
+
+    @Test
+    void modelGroupNullQNameStaysWithinLoaderException() throws Exception {
+        // name.getNamespaceURI() used to run before the try, so a null name
+        // escaped as a raw NullPointerException instead of SchemaTypeLoaderException
+        XsbReader reader = readerForNullQName();
+        assertThrows(SchemaTypeLoaderException.class, reader::finishLoadingModelGroup);
+    }
+
+    @Test
+    void attributeGroupNullQNameStaysWithinLoaderException() throws Exception {
+        XsbReader reader = readerForNullQName();
+        assertThrows(SchemaTypeLoaderException.class, reader::finishLoadingAttributeGroup);
+    }
+}