fix(column-bulk): make column grid sort null-safe (follow-up to #29699)

openmetadata-service/src/main/java/org/openmetadata/service/search/ColumnMetadataGrouper.java

@@ -40,6 +40,11 @@ public static List<ColumnGridItem> groupColumns(
 
     for (Map.Entry<String, List<ColumnWithContext>> entry : columnsByName.entrySet()) {
       String columnName = entry.getKey();
+      if (columnName == null) {
+        // A column with no name isn't a valid grid row (columnName is required in the response);
+        // skip the malformed bucket so we return the remaining valid columns.
+        continue;
+      }
       List<ColumnWithContext> occurrences = entry.getValue();
 
       Map<String, ColumnMetadataGroup> groups = new HashMap<>();
@@ -106,9 +111,12 @@ public static List<ColumnGridItem> groupColumns(
     // guaranteed (current callers build it as a HashMap), so sort here for a stable alphabetical
     // order. Case-insensitive for natural listing, with a case-sensitive tie-breaker so names that
     // differ only in case (e.g. "Name"/"name") stay stable instead of relying on map order.
+    // nullsLast guards against a null column name (e.g. a null map key) rather than throwing.
     gridItems.sort(
-        Comparator.comparing(ColumnGridItem::getColumnName, String.CASE_INSENSITIVE_ORDER)
-            .thenComparing(ColumnGridItem::getColumnName));
+        Comparator.comparing(
+                ColumnGridItem::getColumnName, Comparator.nullsLast(String.CASE_INSENSITIVE_ORDER))
+            .thenComparing(
+                ColumnGridItem::getColumnName, Comparator.nullsLast(Comparator.naturalOrder())));
 
     return gridItems;
   }

openmetadata-service/src/test/java/org/openmetadata/service/search/ColumnMetadataGrouperTest.java

@@ -403,6 +403,22 @@ void testGroupColumns_caseOnlyCollisionsAreDeterministic() {
     assertEquals(List.of("Name", "name"), actual);
   }
 
+  @Test
+  void testGroupColumns_nullColumnNameIsSkipped() {
+    // A null column name (e.g. a null map key) is dropped, not returned with a null required field,
+    // and must not throw. The remaining valid columns still come back sorted.
+    Map<String, List<ColumnMetadataGrouper.ColumnWithContext>> columnsByName =
+        new LinkedHashMap<>();
+    columnsByName.put("beta", singleOccurrence("beta"));
+    columnsByName.put(null, singleOccurrence(null));
+    columnsByName.put("alpha", singleOccurrence("alpha"));
+
+    List<ColumnGridItem> result = ColumnMetadataGrouper.groupColumns(columnsByName);
+
+    List<String> actual = result.stream().map(ColumnGridItem::getColumnName).toList();
+    assertEquals(List.of("alpha", "beta"), actual);
+  }
+
   private static List<ColumnMetadataGrouper.ColumnWithContext> singleOccurrence(String columnName) {
     Column column = new Column();
     column.setName(columnName);