Fix a little spot bugs problem

Author: jeffgbutler

src/main/java/org/mybatis/dynamic/sql/util/ValueMapping.java

@@ -1,5 +1,5 @@
 /**
- *    Copyright 2016-2017 the original author or authors.
+ *    Copyright 2016-2019 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.
@@ -23,8 +23,9 @@ public class ValueMapping<T> extends AbstractColumnMapping implements UpdateMapp
 
     private Supplier<T> valueSupplier;
 
-    private ValueMapping(SqlColumn<T> column) {
+    private ValueMapping(SqlColumn<T> column, Supplier<T> valueSupplier) {
         super(column);
+        this.valueSupplier = valueSupplier;
     }
 
     public T value() {
@@ -37,8 +38,7 @@ public <R> R accept(UpdateMappingVisitor<R> visitor) {
     }
 
     public static <T> ValueMapping<T> of(SqlColumn<T> column, Supplier<T> valueSupplier) {
-        ValueMapping<T> mapping = new ValueMapping<>(column);
-        mapping.valueSupplier = valueSupplier;
+        ValueMapping<T> mapping = new ValueMapping<>(column, valueSupplier);
         return mapping;
     }
 }