fixing patch issue r3labs#63

Author: jdmeyer3

change_value.go

@@ -123,6 +123,10 @@ func (c *ChangeValue) Set(value reflect.Value, convertCompatibleTypes bool) {
 			}
 			c.target.Set(value.Convert(c.target.Type()))
 		} else {
+			if !value.IsValid() && (c.target.Kind() == reflect.Ptr || c.target.Kind() == reflect.Interface) {
+				c.target.Set(reflect.Zero(c.target.Type()))
+				return
+			}
 			c.target.Set(value)
 		}
 		c.SetFlag(FlagApplied)

diff_test.go

@@ -73,6 +73,7 @@ type tstruct struct {
 	Map             map[string]string `diff:"map"`
 	Time            time.Time         `diff:"time"`
 	Pointer         *string           `diff:"pointer"`
+	ValuesPointer   *[]string         `diff:"values_pointer"`
 	Ignored         bool              `diff:"-"`
 	Identifiables   []tistruct        `diff:"identifiables"`
 	Unidentifiables []tuistruct       `diff:"unidentifiables"`
@@ -84,6 +85,10 @@ func sptr(s string) *string {
 	return &s
 }
 
+func saptr(s []string) *[]string {
+	return &s
+}
+
 func TestDiff(t *testing.T) {
 	cases := []struct {
 		Name      string

patch_test.go

@@ -123,6 +123,13 @@ func TestPatch(t *testing.T) {
 			},
 			nil,
 		},
+		{
+			"struct-string-slice-pointer-nil-update", &tstruct{ValuesPointer: saptr([]string{"foo"})}, &tstruct{ValuesPointer: nil},
+			Changelog{
+				Change{Type: UPDATE, Path: []string{"values_pointer"}, From:  sptr("test"), To: nil},
+			},
+			nil,
+		},		
 		{
 			"struct-generic-slice-insert", &tstruct{Values: []string{"one"}}, &tstruct{Values: []string{"one", "two"}},
 			Changelog{