Fix panic on test op

Author: erickertz

patch.go

@@ -688,7 +688,7 @@ func (p Patch) test(doc *container, op Operation) error {
 	}
 
 	if val == nil {
-		if op.value().raw == nil {
+		if op.value() == nil || op.value().raw == nil {
 			return nil
 		}
 		return errors.Wrapf(ErrTestFailed, "testing value %s failed", path)

patch_test.go

@@ -496,6 +496,12 @@ var TestCases = []TestCase{
 		false,
 		"/foo",
 	},
+	{
+		`{ "baz": [] }`,
+		`[ { "op": "test", "path": "/foo"} ]`,
+		true,
+		"/foo",
+	},
 }
 
 func TestAllTest(t *testing.T) {

v5/patch.go

@@ -965,7 +965,7 @@ func (p Patch) test(doc *container, op Operation, options *ApplyOptions) error {
 	}
 
 	if val == nil {
-		if op.value().raw == nil {
+		if op.value() == nil || op.value().raw == nil {
 			return nil
 		}
 		return errors.Wrapf(ErrTestFailed, "testing value %s failed", path)

v5/patch_test.go

@@ -571,6 +571,13 @@ var Cases = []Case{
 }`,
 		false, true,
 	},
+	{
+		`{"baz": []}`,
+		`[ { "op": "test", "path": "/foo" } ]`,
+		`{"baz": []}`,
+		false,
+		false,
+	},
 }
 
 type BadCase struct {