Little code cleanup after merges

Author: jeffgbutler

src/main/java/org/mybatis/dynamic/sql/SqlBuilder.java

@@ -188,6 +188,7 @@ static Sum sum(BasicColumn column) {
     }
 
     // functions
+    @SafeVarargs
     static <T extends Number> Add<T> add(BindableColumn<T>... columns) {
         return Add.of(Arrays.asList(columns));
     }

src/main/java/org/mybatis/dynamic/sql/select/function/Add.java

@@ -16,10 +16,9 @@
 package org.mybatis.dynamic.sql.select.function;
 
 import java.sql.JDBCType;
+import java.util.ArrayList;
 import java.util.List;
-import java.util.Objects;
 import java.util.Optional;
-import java.util.StringJoiner;
 import java.util.stream.Collectors;
 
 import org.mybatis.dynamic.sql.BindableColumn;
@@ -28,10 +27,10 @@
 public class Add<T extends Number> implements BindableColumn<T> {
 
     private String alias;
-    private List<BindableColumn<T>> columns;
+    private List<BindableColumn<T>> columns = new ArrayList<>();
 
     private Add(List<BindableColumn<T>> columns) {
-        this.columns = Objects.requireNonNull(columns);
+        this.columns.addAll(columns);
     }
 
     @Override
@@ -42,8 +41,8 @@ public Optional<String> alias() {
     @Override
     public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
         return columns.stream()
-                      .map(column -> column.renderWithTableAlias(tableAliasCalculator))
-                      .collect(Collectors.joining(" + "));
+                .map(column -> column.renderWithTableAlias(tableAliasCalculator))
+                .collect(Collectors.joining(" + "));
     }
 
     @Override

src/test/java/examples/groupby/GroupByTest.java

@@ -1,5 +1,5 @@
 /**
- *    Copyright 2016-2017 the original author or authors.
+ *    Copyright 2016-2018 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.