API: Handle null partition values in ResidualEvaluator startsWith/notStartsWith

api/src/main/java/org/apache/iceberg/expressions/ResidualEvaluator.java

@@ -212,16 +212,16 @@ public <T> Expression notIn(BoundReference<T> ref, Set<T> literalSet) {
 
     @Override
     public <T> Expression startsWith(BoundReference<T> ref, Literal<T> lit) {
-      return ((String) ref.eval(struct)).startsWith((String) lit.value())
-          ? alwaysTrue()
-          : alwaysFalse();
+      String value = (String) ref.eval(struct);
+      return value != null && value.startsWith((String) lit.value()) ? alwaysTrue() : alwaysFalse();
     }
 
     @Override
     public <T> Expression notStartsWith(BoundReference<T> ref, Literal<T> lit) {
-      return ((String) ref.eval(struct)).startsWith((String) lit.value())
-          ? alwaysFalse()
-          : alwaysTrue();
+      String value = (String) ref.eval(struct);
+      return value == null || !value.startsWith((String) lit.value())
+          ? alwaysTrue()
+          : alwaysFalse();
     }
 
     @Override

api/src/test/java/org/apache/iceberg/transforms/TestResiduals.java

@@ -289,6 +289,44 @@ public void testNotInWithNullStringPartition() {
     assertThat(residual).as("null not in [a, b, c] => true").isEqualTo(alwaysTrue());
   }
 
+  @Test
+  public void testStartsWithWithNullStringPartition() {
+    Schema schema = new Schema(Types.NestedField.optional(50, "category", Types.StringType.get()));
+
+    PartitionSpec spec = PartitionSpec.builderFor(schema).identity("category").build();
+
+    ResidualEvaluator resEval =
+        ResidualEvaluator.of(spec, Expressions.startsWith("category", "a"), true);
+
+    Expression residual = resEval.residualFor(Row.of("abc"));
+    assertThat(residual).isEqualTo(alwaysTrue());
+
+    residual = resEval.residualFor(Row.of("bcd"));
+    assertThat(residual).isEqualTo(alwaysFalse());
+
+    residual = resEval.residualFor(Row.of((Object) null));
+    assertThat(residual).as("null startsWith a => false").isEqualTo(alwaysFalse());
+  }
+
+  @Test
+  public void testNotStartsWithWithNullStringPartition() {
+    Schema schema = new Schema(Types.NestedField.optional(50, "category", Types.StringType.get()));
+
+    PartitionSpec spec = PartitionSpec.builderFor(schema).identity("category").build();
+
+    ResidualEvaluator resEval =
+        ResidualEvaluator.of(spec, Expressions.notStartsWith("category", "a"), true);
+
+    Expression residual = resEval.residualFor(Row.of("bcd"));
+    assertThat(residual).isEqualTo(alwaysTrue());
+
+    residual = resEval.residualFor(Row.of("abc"));
+    assertThat(residual).isEqualTo(alwaysFalse());
+
+    residual = resEval.residualFor(Row.of((Object) null));
+    assertThat(residual).as("null notStartsWith a => true").isEqualTo(alwaysTrue());
+  }
+
   @Test
   public void testIsNaN() {
     Schema schema =