From 1b95334f87e7f0cb8d8693cee0cbaea31ff562da Mon Sep 17 00:00:00 2001
From: Ewan Chou <coocood@gmail.com>
Date: Thu, 24 Sep 2015 16:29:29 +0800
Subject: [PATCH] expression: fix import and BaseVisitor

---
 expression/helper.go        |  2 --
 expression/visitor.go       | 19 +++++++++++++------
 expression/visitor_ident.go |  7 -------
 3 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/expression/helper.go b/expression/helper.go
index fb0009783f..be573e3fba 100644
--- a/expression/helper.go
+++ b/expression/helper.go
@@ -27,9 +27,7 @@ import (
 	"time"
 
 	"github.com/juju/errors"
-	"github.com/ngaut/log"
 	"github.com/pingcap/tidb/context"
-
 	"github.com/pingcap/tidb/expression/builtin"
 	"github.com/pingcap/tidb/model"
 	mysql "github.com/pingcap/tidb/mysqldef"
diff --git a/expression/visitor.go b/expression/visitor.go
index c91623f236..7f31259dc0 100644
--- a/expression/visitor.go
+++ b/expression/visitor.go
@@ -181,9 +181,11 @@ func (bv *BaseVisitor) VisitExistsSubQuery(es *ExistsSubQuery) (Expression, erro
 // VisitFunctionCase implements Visitor interface.
 func (bv *BaseVisitor) VisitFunctionCase(f *FunctionCase) (Expression, error) {
 	var err error
-	f.Value, err = f.Value.Accept(bv.V)
-	if err != nil {
-		return f, errors.Trace(err)
+	if f.Value != nil {
+		f.Value, err = f.Value.Accept(bv.V)
+		if err != nil {
+			return f, errors.Trace(err)
+		}
 	}
 	for i := range f.WhenClauses {
 		_, err = f.WhenClauses[i].Accept(bv.V)
@@ -191,9 +193,11 @@ func (bv *BaseVisitor) VisitFunctionCase(f *FunctionCase) (Expression, error) {
 			return f, errors.Trace(err)
 		}
 	}
-	f.ElseClause, err = f.ElseClause.Accept(bv.V)
-	if err != nil {
-		return f, errors.Trace(err)
+	if f.ElseClause != nil {
+		f.ElseClause, err = f.ElseClause.Accept(bv.V)
+		if err != nil {
+			return f, errors.Trace(err)
+		}
 	}
 	return f, nil
 }
@@ -229,6 +233,9 @@ func (bv *BaseVisitor) VisitFunctionSubstring(ss *FunctionSubstring) (Expression
 	if err != nil {
 		return ss, errors.Trace(err)
 	}
+	if ss.Len == nil {
+		return ss, nil
+	}
 	ss.Len, err = ss.Len.Accept(bv.V)
 	if err != nil {
 		return ss, errors.Trace(err)
diff --git a/expression/visitor_ident.go b/expression/visitor_ident.go
index 2757e1f717..fadd6a099f 100644
--- a/expression/visitor_ident.go
+++ b/expression/visitor_ident.go
@@ -13,13 +13,6 @@
 
 package expression
 
-import (
-	"strings"
-
-	"github.com/juju/errors"
-	"github.com/pingcap/tidb/expression/builtin"
-)
-
 // IdentEvalVisitor converts Ident expression to value expression.
 type IdentEvalVisitor struct {
 	BaseVisitor