From 8ef62a3f134b3d26edd595dc0d9f499fa0e23b37 Mon Sep 17 00:00:00 2001
From: ffccites <99155080+PDGGK@users.noreply.github.com>
Date: Mon, 3 Aug 2026 16:55:39 +1000
Subject: [PATCH] Fix Row.toString NPE on a null nested inside an array, map or
 row

toPrettyRowString drops a row's own null fields, but every recursive call
hands the raw element to toPrettyFieldValueString, which dereferences it:
a null String hits string.replace, a null Row hits row.getValues, and a
null array or map hits value.getClass. Only the numeric and boolean
branches survive, because Objects.toString already renders null as "null".

Return "null" for a null value instead, which is what those numeric
branches have always produced.

Row.toString has routed through this printer since 2.69.0, so the NPE
fires from logging, PAssert messages and debugger inspection - usually
while a pipeline is already reporting a different problem.

Fixes #21063
---
 .../apache/beam/sdk/schemas/SchemaUtils.java  |  7 +++
 .../beam/sdk/schemas/SchemaUtilsTest.java     | 43 +++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/SchemaUtils.java b/sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/SchemaUtils.java
index c8773ce2c232..88809182efcd 100644
--- a/sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/SchemaUtils.java
+++ b/sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/SchemaUtils.java
@@ -238,6 +238,13 @@ static String toPrettyOptionsString(Schema.Options options, String prefix) {
   }
 
   static String toPrettyFieldValueString(Schema.FieldType fieldType, Object value, String prefix) {
+    if (value == null) {
+      // toPrettyRowString drops a row's own null fields, but a null nested inside an array, an
+      // iterable, a map or a row has a position and has to be rendered. The numeric and boolean
+      // branches below already render one as "null" via Objects.toString, so do the same for the
+      // remaining types rather than dereferencing the value.
+      return "null";
+    }
     String nextPrefix = prefix + INDENT;
     switch (fieldType.getTypeName()) {
       case BYTE:
diff --git a/sdks/java/core/src/test/java/org/apache/beam/sdk/schemas/SchemaUtilsTest.java b/sdks/java/core/src/test/java/org/apache/beam/sdk/schemas/SchemaUtilsTest.java
index 45c06f65aaa7..c34832f58fb8 100644
--- a/sdks/java/core/src/test/java/org/apache/beam/sdk/schemas/SchemaUtilsTest.java
+++ b/sdks/java/core/src/test/java/org/apache/beam/sdk/schemas/SchemaUtilsTest.java
@@ -18,8 +18,13 @@
 package org.apache.beam.sdk.schemas;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
 import org.apache.beam.sdk.schemas.Schema.FieldType;
+import org.apache.beam.sdk.values.Row;
 import org.junit.Test;
 
 /** Tests for {@link org.apache.beam.sdk.schemas.SchemaUtils}. */
@@ -104,4 +109,42 @@ public void testWidenMap() {
             .build();
     assertEquals(expected, SchemaUtils.mergeWideningNullable(schema1, schema2));
   }
+
+  @Test
+  public void testToPrettyStringRendersNullInsideArray() {
+    Schema schema =
+        Schema.builder().addArrayField("a", FieldType.STRING.withNullable(true)).build();
+    Row row = Row.withSchema(schema).addValue(Arrays.asList("x", null)).build();
+    assertTrue(row.toString(), row.toString().contains("null"));
+  }
+
+  @Test
+  public void testToPrettyStringRendersNullMapValue() {
+    Schema schema =
+        Schema.builder()
+            .addMapField("m", FieldType.STRING, FieldType.STRING.withNullable(true))
+            .build();
+    Map<String, String> map = new HashMap<>();
+    map.put("k", null);
+    Row row = Row.withSchema(schema).addValue(map).build();
+    assertTrue(row.toString(), row.toString().contains("null"));
+  }
+
+  @Test
+  public void testToPrettyStringRendersNullRowInsideArray() {
+    Schema inner = Schema.builder().addStringField("s").build();
+    Schema schema =
+        Schema.builder().addArrayField("a", FieldType.row(inner).withNullable(true)).build();
+    Row row = Row.withSchema(schema).addValue(Arrays.asList((Row) null)).build();
+    assertTrue(row.toString(), row.toString().contains("null"));
+  }
+
+  @Test
+  public void testToPrettyStringRendersNullInsideArrayOfInts() {
+    Schema schema = Schema.builder().addArrayField("a", FieldType.INT32.withNullable(true)).build();
+    Row row = Row.withSchema(schema).addValue(Arrays.asList(1, null)).build();
+    String rendered = row.toString();
+    assertTrue(rendered, rendered.contains("1"));
+    assertTrue(rendered, rendered.contains("null"));
+  }
 }