From a5df74aab0efb032ca893c048330abcad0b78e6f Mon Sep 17 00:00:00 2001
From: Brett Buddin <brett@buddin.org>
Date: Wed, 7 Aug 2019 17:12:57 -0400
Subject: [PATCH 1/4] Conform to RFC6902 replacement semantics.

A "replace" patch operation referencing a key that does not exist in the
target object are currently being accepted; ultimately becoming "add"
operations on the target object. This is incorrect per the
specification:

From https://tools.ietf.org/html/rfc6902#section-4.3 section about
"replace":

    The target location MUST exist for the operation to be successful.

This corrects the behavior by returning an error in this situation.
---
 patch.go      | 10 +++++++---
 patch_test.go |  4 ++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/patch.go b/patch.go
index 8f75549..c105632 100644
--- a/patch.go
+++ b/patch.go
@@ -384,13 +384,17 @@ func (d *partialDoc) add(key string, val *lazyNode) error {
 }
 
 func (d *partialDoc) get(key string) (*lazyNode, error) {
-	return (*d)[key], nil
+	v, ok := (*d)[key]
+	if !ok {
+		return v, errors.Wrapf(ErrMissing, "unable to get nonexistent key: %s", key)
+	}
+	return v, nil
 }
 
 func (d *partialDoc) remove(key string) error {
 	_, ok := (*d)[key]
 	if !ok {
-		return errors.Wrapf(ErrMissing, "Unable to remove nonexistent key: %s", key)
+		return errors.Wrapf(ErrMissing, "unable to remove nonexistent key: %s", key)
 	}
 
 	delete(*d, key)
@@ -612,7 +616,7 @@ func (p Patch) test(doc *container, op Operation) error {
 	}
 
 	val, err := con.get(key)
-	if err != nil {
+	if err != nil && errors.Cause(err) != ErrMissing {
 		return errors.Wrapf(err, "error in test for path: '%s'", path)
 	}
 
diff --git a/patch_test.go b/patch_test.go
index 3a45150..30f6176 100644
--- a/patch_test.go
+++ b/patch_test.go
@@ -332,6 +332,10 @@ var BadCases = []BadCase{
 		`{ "foo": [ "all", "grass", "cows", "eat" ] }`,
 		`[ { "op": "move", "from": "/foo/1", "path": "/foo/4" } ]`,
 	},
+	{
+		`{ "baz": "qux" }`,
+		`[ { "op": "replace", "path": "/foo", "value": "bar" } ]`,
+	},
 }
 
 // This is not thread safe, so we cannot run patch tests in parallel.

From caa7f266ac971d84049d2a618644979d26114ac8 Mon Sep 17 00:00:00 2001
From: Brett Buddin <brett@buddin.org>
Date: Mon, 4 Nov 2019 13:16:59 -0500
Subject: [PATCH 2/4] Test for copying non-existent key.

---
 patch_test.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/patch_test.go b/patch_test.go
index 30f6176..66e5bd3 100644
--- a/patch_test.go
+++ b/patch_test.go
@@ -336,6 +336,11 @@ var BadCases = []BadCase{
 		`{ "baz": "qux" }`,
 		`[ { "op": "replace", "path": "/foo", "value": "bar" } ]`,
 	},
+	// Can't copy from non-existent "from" key.
+	{
+		`{ "foo": "bar"}`,
+		`[{"op": "copy", "path": "/qux", "from": "/baz"}]`,
+	},
 }
 
 // This is not thread safe, so we cannot run patch tests in parallel.

From c235ce89e1e02a76eac0be921e6e8fe12d9c6120 Mon Sep 17 00:00:00 2001
From: Brett Buddin <brett@buddin.org>
Date: Mon, 4 Nov 2019 13:17:14 -0500
Subject: [PATCH 3/4] Test for testing non-existent and null-value keys.

---
 patch_test.go | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/patch_test.go b/patch_test.go
index 66e5bd3..69851bc 100644
--- a/patch_test.go
+++ b/patch_test.go
@@ -468,6 +468,18 @@ var TestCases = []TestCase{
 		false,
 		"/foo",
 	},
+	{
+		`{ "foo": "bar" }`,
+		`[ { "op": "test", "path": "/baz", "value": "bar" } ]`,
+		false,
+		"/baz",
+	},
+	{
+		`{ "foo": "bar" }`,
+		`[ { "op": "test", "path": "/baz", "value": null } ]`,
+		true,
+		"/baz",
+	},
 }
 
 func TestAllTest(t *testing.T) {

From 266303115221f6a79e03731280f3676b22168d2c Mon Sep 17 00:00:00 2001
From: Brett Buddin <brett@buddin.org>
Date: Mon, 4 Nov 2019 13:20:41 -0500
Subject: [PATCH 4/4] Test for copying null-value key.

---
 patch_test.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/patch_test.go b/patch_test.go
index 69851bc..8e20cf3 100644
--- a/patch_test.go
+++ b/patch_test.go
@@ -186,6 +186,11 @@ var Cases = []Case{
 		`[{"op": "copy", "path": "/foo/0", "from": "/foo"}]`,
 		`{ "foo": [["bar"], "bar"]}`,
 	},
+	{
+		`{ "foo": null}`,
+		`[{"op": "copy", "path": "/bar", "from": "/foo"}]`,
+		`{ "foo": null, "bar": null}`,
+	},
 	{
 		`{ "foo": ["bar","qux","baz"]}`,
 		`[ { "op": "remove", "path": "/foo/-2"}]`,