Fix wrong asserted code in ConvertingCursor.

Pull Request: spring-projects#2696

Author: m1ngyuan

src/main/java/org/springframework/data/redis/core/ConvertingCursor.java

@@ -40,8 +40,8 @@ public class ConvertingCursor<S, T> implements Cursor<T> {
 	 */
 	public ConvertingCursor(Cursor<S> cursor, Converter<S, T> converter) {
 
-		Assert.notNull(cursor, "Cursor delegate must not be 'null'.");
-		Assert.notNull(cursor, "Converter must not be 'null'.");
+		Assert.notNull(cursor, "Cursor delegate must not be 'null'");
+		Assert.notNull(converter, "Converter must not be 'null'");
 		this.delegate = cursor;
 		this.converter = converter;
 	}