add new empty method and add tests for AmmClawbackFlags

xrpl4j-core/src/main/java/org/xrpl/xrpl4j/model/flags/AmmClawbackFlags.java

@@ -39,6 +39,18 @@ public class AmmClawbackFlags extends TransactionFlags {
   private AmmClawbackFlags(long value) {
     super(value);
   }
+  private AmmClawbackFlags() {
+  }
+
+  /**
+   * Construct an empty instance of {@link AmmClawbackFlags}. Transactions with empty flags will
+   * not be serialized with a {@code Flags} field.
+   *
+   * @return An empty {@link AmmClawbackFlags}.
+   */
+  public static AmmClawbackFlags empty() {
+    return new AmmClawbackFlags();
+  }
 
   /**
    * Whether the {@code tfClawTwoAssets} flag is set.

xrpl4j-core/src/test/java/org/xrpl/xrpl4j/model/flags/AmmClawbackFlagsTest.java

@@ -0,0 +1,49 @@
+package org.xrpl.xrpl4j.model.flags;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import org.json.JSONException;
+import org.junit.jupiter.api.Test;
+
+class AmmClawbackFlagsTest extends AbstractFlagsTest {
+
+  @Test
+  void testFlagWithValue() {
+    AmmClawbackFlags flags = AmmClawbackFlags.CLAW_TWO_ASSETS;
+    assertThat(flags.isEmpty()).isFalse();
+
+    assertThat(flags.tfClawTwoAssets()).isTrue();
+    assertThat(flags.tfFullyCanonicalSig()).isFalse();
+    assertThat(flags.getValue()).isEqualTo(1L);
+  }
+
+  @Test
+  void testEmptyFlags() {
+    AmmClawbackFlags flags = AmmClawbackFlags.empty();
+    assertThat(flags.isEmpty()).isTrue();
+
+    assertThat(flags.tfClawTwoAssets()).isFalse();
+    assertThat(flags.tfFullyCanonicalSig()).isFalse();
+    assertThat(flags.getValue()).isZero();
+  }
+
+  @Test
+  void testJson() throws JSONException, JsonProcessingException {
+    TransactionFlagsWrapper wrapper = TransactionFlagsWrapper.of(AmmClawbackFlags.CLAW_TWO_ASSETS);
+    String json = String.format("{\n" +
+        "               \"flags\": %s\n" +
+        "}", AmmClawbackFlags.CLAW_TWO_ASSETS.getValue());
+
+    assertCanSerializeAndDeserialize(wrapper, json);
+  }
+  @Test
+  void testEmptyJson() throws JSONException, JsonProcessingException {
+    AmmClawbackFlags flags = AmmClawbackFlags.empty();
+    AbstractFlagsTest.TransactionFlagsWrapper wrapper = AbstractFlagsTest.TransactionFlagsWrapper.of(flags);
+    String json = "{\n" +
+        "}";
+
+    assertCanSerializeAndDeserialize(wrapper, json);
+  }
+}