Fix potential lambda argument mismatch (#448)

api/src/main/java/jakarta/el/ELContext.java

diff --git a/api/src/main/java/jakarta/el/ELContext.java b/api/src/main/java/jakarta/el/ELContext.java
index ef0f6e3..bfc5ce8 100644
--- a/api/src/main/java/jakarta/el/ELContext.java
+++ b/api/src/main/java/jakarta/el/ELContext.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2024 Oracle and/or its affiliates and others.
+ * Copyright (c) 1997, 2026 Oracle and/or its affiliates and others.
  * All rights reserved.
  * Copyright 2004 The Apache Software Foundation
  *
@@ -72,7 +72,7 @@
  * @see ImportHandler
  * @see LambdaExpression
  * @see StandardELContext
- * 
+ *
  * @since Jakarta Expression Language 2.1 and Jakarta Expression Language 3.0
  */
 public abstract class ELContext {
@@ -207,7 +207,7 @@
      * Retrieves the <code>ImportHandler</code> associated with this <code>ELContext</code>.
      *
      * @return The import handler to manage imports of classes and packages.
-     * 
+     *
      * @since Jakarta Expression Language 3.0
      */
     public ImportHandler getImportHandler() {
@@ -357,7 +357,7 @@
      *
      * @param arg The formal parameter for the Lambda argument
      * @return The object associated with formal parameter. Null if no object has been associated with the parameter.
-     * 
+     *
      * @since Jakarta Expression Language 3.0
      */
     public Object getLambdaArgument(String arg) {
@@ -368,7 +368,7 @@
         for (int i = lambdaArgs.size() - 1; i >= 0; i--) {
             Map<String, Object> lmap = lambdaArgs.elementAt(i);
             Object v = lmap.get(arg);
-            if (v != null) {
+            if (v != null || lmap.containsKey(arg)) {
                 return v;
             }
         }
@@ -381,7 +381,7 @@
      * will be in scope during the evaluation of the Lambda expression.
      *
      * @param args The Lambda arguments map
-     * 
+     *
      * @since Jakarta Expression Language 3.0
      */
     public void enterLambdaScope(Map<String, Object> args) {
@@ -413,7 +413,7 @@
      * @param <T> The target type for the conversion.
      * @param obj The object to convert.
      * @param targetType The target type for the conversion.
-     * 
+     *
      * @return object converted to <code>targetType</code>
      * @throws ELException thrown if errors occur.
      *

api/src/test/java/jakarta/el/TestELContext.java

diff --git a/api/src/test/java/jakarta/el/TestELContext.java b/api/src/test/java/jakarta/el/TestELContext.java
new file mode 100644
index 0000000..0e22ef7
--- /dev/null
+++ b/api/src/test/java/jakarta/el/TestELContext.java
@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0, which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the
+ * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
+ * version 2 with the GNU Classpath Exception, which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ */
+package jakarta.el;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class TestELContext {
+
+    private static final String NAME = "x";
+    private static final String VALUE_NON_NULL = "x";
+    private static final String VALUE_NULL = null;
+
+
+    @Test
+    public void testLambdaScopeWithNullParameter() {
+        ELContext elContext = new SimpleELContextImpl();
+
+        // Set up parameters for outer scope
+        Map<String,Object> outerParams = new HashMap<>();
+        outerParams.put(NAME, VALUE_NON_NULL);
+
+        // Set up parameters for innerscope
+        Map<String,Object> innerParams = new HashMap<>();
+        innerParams.put(NAME, VALUE_NULL);
+
+        // Enter outer scope
+        elContext.enterLambdaScope(outerParams);
+
+        // Should see outer, non-null value
+        Assertions.assertEquals(VALUE_NON_NULL, elContext.getLambdaArgument(NAME));
+
+        // Enter inner scope
+        elContext.enterLambdaScope(innerParams);
+
+        // Should see inner, null value
+        Assertions.assertNull(elContext.getLambdaArgument(NAME));
+    }
+
+
+    private static class SimpleELContextImpl extends ELContext {
+
+        @Override
+        public ELResolver getELResolver() {
+            return null;
+        }
+
+        @Override
+        public FunctionMapper getFunctionMapper() {
+            return null;
+        }
+
+        @Override
+        public VariableMapper getVariableMapper() {
+            return null;
+        }
+    }
+}

spec/src/main/asciidoc/expression-language-spec-body.adoc

diff --git a/spec/src/main/asciidoc/expression-language-spec-body.adoc b/spec/src/main/asciidoc/expression-language-spec-body.adoc
index 2f0921c..84ee619 100644
--- a/spec/src/main/asciidoc/expression-language-spec-body.adoc
+++ b/spec/src/main/asciidoc/expression-language-spec-body.adoc
@@ -3186,6 +3186,10 @@
   instances in the list of conditions that cause the empty operator to return
   true.
 
+* https://github.com/jakartaee/expression-language/issues/447[#447]
+  Fix an issue in the `ELContext` class so that expression such as
+  `(x -> (x -> x)(null))(42)` correctly evaluate to `null` rather than `42`.
+
 === Changes between 6.0 and 5.0
 
 * The EL API requires Java 17 as a minimum.