Core: Fix NPE of generateRandomMetrics in FileGenerationUtil

core/src/test/java/org/apache/iceberg/FileGenerationUtil.java

@@ -280,9 +280,13 @@ private static long generateContentLength() {
   }
 
   private static Pair<ByteBuffer, ByteBuffer> generateBounds(PrimitiveType type, MetricsMode mode) {
-    Comparator<Object> cmp = Comparators.forType(type);
     Object value1 = generateBound(type, mode);
     Object value2 = generateBound(type, mode);
+
+    if (value1 == null || value2 == null) {
+      return Pair.of(null, null);
+    }
+    Comparator<Object> cmp = Comparators.forType(type);
     if (cmp.compare(value1, value2) > 0) {
       ByteBuffer lowerBuffer = Conversions.toByteBuffer(type, value2);
       ByteBuffer upperBuffer = Conversions.toByteBuffer(type, value1);

core/src/test/java/org/apache/iceberg/TestFileGenerationUtil.java

@@ -31,6 +31,8 @@
 import org.apache.iceberg.types.Types;
 import org.apache.iceberg.types.Types.NestedField;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 
 public class TestFileGenerationUtil {
 
@@ -85,6 +87,23 @@ public void testBoundsWithSpecificValues() {
     assertThat(actualIntUpper).isEqualTo(intUpper);
   }
 
+  @ParameterizedTest
+  @ValueSource(strings = {"none", "counts", "truncate(16)", "full"})
+  @SuppressWarnings("deprecation")
+  void testBoundsForAllMetricsModes(String metricsMode) {
+    MetricsConfig metricsConfig =
+        MetricsConfig.fromProperties(
+            ImmutableMap.of(TableProperties.DEFAULT_WRITE_METRICS_MODE, metricsMode));
+    Metrics metrics =
+        FileGenerationUtil.generateRandomMetrics(
+            SCHEMA,
+            metricsConfig,
+            ImmutableMap.of() /* no lower bounds */,
+            ImmutableMap.of() /* no upper bounds */);
+
+    checkBounds(metrics, metricsConfig);
+  }
+
   private void checkBounds(Metrics metrics, MetricsConfig metricsConfig) {
     for (NestedField field : SCHEMA.columns()) {
       MetricsMode mode = metricsConfig.columnMode(field.name());