improve sql wall

src/main/java/com/alibaba/druid/sql/ast/expr/SQLMethodInvokeExpr.java

@@ -67,6 +67,13 @@ public class SQLMethodInvokeExpr extends SQLExprImpl implements Serializable {
     public List<SQLExpr> getParameters() {
         return this.parameters;
     }
+    
+    public void addParameter(SQLExpr param) {
+        if (param != null) {
+            param.setParent(this);
+        }
+        this.parameters.add(param);
+    }
 
     public void output(StringBuffer buf) {
         if (this.owner != null) {