Fix CopyArgs rendering for REPLACE #1777

Lettuce now correctly checks if the replace flag was set using a boolean check instead of non-null.

src/main/java/io/lettuce/core/CopyArgs.java

@@ -31,7 +31,7 @@ public class CopyArgs implements CompositeArgument {
 
 	private Long destinationDb;
 
-	private Boolean replace;
+    private boolean replace;
 
 	/**
 	 * Builder entry points for {@link CopyArgs}.
@@ -95,7 +95,7 @@ public <K, V> void build(CommandArgs<K, V> args) {
 			args.add(CommandKeyword.DB).add(destinationDb);
 		}
 
-		if(replace != null) {
+        if (replace) {
 			args.add(CommandKeyword.REPLACE);
 		}
 	}

src/test/java/io/lettuce/core/CopyArgsUnitTests.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.lettuce.core;
+
+import io.lettuce.core.codec.StringCodec;
+import io.lettuce.core.protocol.CommandArgs;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.*;
+
+/**
+ * Unit tests for {@link CopyArgs}.
+ *
+ * @author Mark Paluch
+ */
+class CopyArgsUnitTests {
+
+    @Test
+    void shouldRenderFullArgs() {
+
+        CommandArgs<String, String> args = new CommandArgs<>(StringCodec.UTF8);
+
+        CopyArgs.Builder.destinationDb(1).replace(true).build(args);
+
+        assertThat(args.toCommandString()).isEqualTo("DB 1 REPLACE");
+    }
+
+    @Test
+    void shouldRenderNoArgs() {
+
+        CommandArgs<String, String> args = new CommandArgs<>(StringCodec.UTF8);
+
+        CopyArgs.Builder.replace(false).build(args);
+
+        assertThat(args.toCommandString()).isEmpty();
+    }
+
+}