From 585471740c575a4b1c5cafcdddd6bb60478b994f Mon Sep 17 00:00:00 2001
From: seethinajayadileep <seethinajayadileep@hotmail.com>
Date: Fri, 6 Mar 2026 23:48:30 +0530
Subject: [PATCH 1/2] Fix duplicate field name handling in
 InstanceCoercer#getFieldWriters

---
 java/src/org/openqa/selenium/json/InstanceCoercer.java | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/java/src/org/openqa/selenium/json/InstanceCoercer.java b/java/src/org/openqa/selenium/json/InstanceCoercer.java
index f0f43a2943c38..588f7718088dd 100644
--- a/java/src/org/openqa/selenium/json/InstanceCoercer.java
+++ b/java/src/org/openqa/selenium/json/InstanceCoercer.java
@@ -126,7 +126,9 @@ private Map<String, TypeAndWriter> getFieldWriters(Constructor<?> constructor) {
                         }
                       };
                   return new TypeAndWriter(type, writer);
-                }));
+                },
+                (existing, ignored) -> existing,
+                java.util.LinkedHashMap::new));
   }
 
   private Map<String, TypeAndWriter> getBeanWriters(Constructor<?> constructor) {

From 79b40cdce5a006cf2da22d684934074cf69092b8 Mon Sep 17 00:00:00 2001
From: seethinajayadileep <seethinajayadileep@hotmail.com>
Date: Sat, 7 Mar 2026 18:11:17 +0530
Subject: [PATCH 2/2] added unit testcase

---
 .../openqa/selenium/json/InstanceCoercer.java |  6 ++++--
 .../org/openqa/selenium/json/JsonTest.java    | 20 +++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/java/src/org/openqa/selenium/json/InstanceCoercer.java b/java/src/org/openqa/selenium/json/InstanceCoercer.java
index 588f7718088dd..87aa260e81ac2 100644
--- a/java/src/org/openqa/selenium/json/InstanceCoercer.java
+++ b/java/src/org/openqa/selenium/json/InstanceCoercer.java
@@ -127,8 +127,10 @@ private Map<String, TypeAndWriter> getFieldWriters(Constructor<?> constructor) {
                       };
                   return new TypeAndWriter(type, writer);
                 },
-                (existing, ignored) -> existing,
-                java.util.LinkedHashMap::new));
+                (existing, replacement) -> {
+                  throw new JsonException(
+                      "Duplicate JSON field name detected while collecting field writers");
+                }));
   }
 
   private Map<String, TypeAndWriter> getBeanWriters(Constructor<?> constructor) {
diff --git a/java/test/org/openqa/selenium/json/JsonTest.java b/java/test/org/openqa/selenium/json/JsonTest.java
index a8470b722f51b..762e50fefe303 100644
--- a/java/test/org/openqa/selenium/json/JsonTest.java
+++ b/java/test/org/openqa/selenium/json/JsonTest.java
@@ -132,6 +132,18 @@ void shouldAllowUserToPopulateFieldsDirectly() {
     assertThat(seen.theName).isEqualTo("fishy");
   }
 
+  @Test
+  void shouldThrowWhenDuplicateFieldNamesExistWithFieldSetting() {
+    String raw = "{\"value\": \"test\"}";
+
+    assertThatThrownBy(() -> new Json().toType(raw, ChildFieldBean.class, BY_FIELD))
+        .isInstanceOf(JsonException.class)
+        .hasMessageStartingWith("Unable to parse: " + raw)
+        .cause()
+        .isInstanceOf(JsonException.class)
+        .hasMessage("Duplicate JSON field name detected while collecting field writers");
+  }
+
   @Test
   void settingFinalFieldsShouldWork() {
     Map<String, String> map = Map.of("theName", "fishy");
@@ -661,6 +673,14 @@ public void setBean(SimpleBean bean) {
     }
   }
 
+  public static class ParentFieldBean {
+    String value;
+  }
+
+  public static class ChildFieldBean extends ParentFieldBean {
+    String value;
+  }
+
   public static class JsonAware {
     private final String convertedValue;