Introduce OutboundRow.clone() method.

Closes #620.

src/main/java/org/springframework/data/r2dbc/mapping/OutboundRow.java

@@ -36,7 +36,7 @@ import org.springframework.util.Assert;
  * @see SqlIdentifier
  * @see Parameter
  */
-public class OutboundRow implements Map<SqlIdentifier, Parameter> {
+public class OutboundRow implements Map<SqlIdentifier, Parameter>, Cloneable {
 
 	private final Map<SqlIdentifier, Parameter> rowAsMap;
 
@@ -61,6 +61,12 @@ public class OutboundRow implements Map<SqlIdentifier, Parameter> {
 		map.forEach((s, Parameter) -> this.rowAsMap.put(SqlIdentifier.unquoted(s), Parameter));
 	}
 
+	private OutboundRow(OutboundRow map) {
+
+		this.rowAsMap = new LinkedHashMap<>(map.size());
+		this.rowAsMap.putAll(map);
+	}
+
 	/**
 	 * Create a {@link OutboundRow} instance initialized with the given key/value pair.
 	 *
@@ -137,6 +143,15 @@ public class OutboundRow implements Map<SqlIdentifier, Parameter> {
 		return this.rowAsMap.isEmpty();
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see java.lang.Object#clone()
+	 */
+	@Override
+	protected OutboundRow clone() {
+		return new OutboundRow(this);
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see java.util.Map#containsKey(java.lang.Object)