From 820a3320be10bc925877afc78cdc0bec97e4f8e2 Mon Sep 17 00:00:00 2001
From: Mike Farah <mikefarah@gmail.com>
Date: Tue, 26 Jan 2021 10:21:16 +1100
Subject: [PATCH] Fixed length of null to be zero

---
 pkg/yqlib/doc/Length.md           | 14 ++++++++++++++
 pkg/yqlib/operator_length.go      |  6 +++++-
 pkg/yqlib/operator_length_test.go | 24 ++++++++++++++++++++++++
 3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/pkg/yqlib/doc/Length.md b/pkg/yqlib/doc/Length.md
index dcd76562..0f7e73d7 100644
--- a/pkg/yqlib/doc/Length.md
+++ b/pkg/yqlib/doc/Length.md
@@ -16,6 +16,20 @@ will output
 3
 ```
 
+## null length
+Given a sample.yml file of:
+```yaml
+a: null
+```
+then
+```bash
+yq eval '.a | length' sample.yml
+```
+will output
+```yaml
+0
+```
+
 ## Map length
 returns number of entries
 
diff --git a/pkg/yqlib/operator_length.go b/pkg/yqlib/operator_length.go
index b9d6dded..70888d2e 100644
--- a/pkg/yqlib/operator_length.go
+++ b/pkg/yqlib/operator_length.go
@@ -17,7 +17,11 @@ func lengthOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *E
 		var length int
 		switch targetNode.Kind {
 		case yaml.ScalarNode:
-			length = len(targetNode.Value)
+			if targetNode.Tag == "!!null" {
+				length = 0
+			} else {
+				length = len(targetNode.Value)
+			}
 		case yaml.MappingNode:
 			length = len(targetNode.Content) / 2
 		case yaml.SequenceNode:
diff --git a/pkg/yqlib/operator_length_test.go b/pkg/yqlib/operator_length_test.go
index 353f2ef8..e9ecc2d0 100644
--- a/pkg/yqlib/operator_length_test.go
+++ b/pkg/yqlib/operator_length_test.go
@@ -14,6 +14,30 @@ var lengthOperatorScenarios = []expressionScenario{
 			"D0, P[a], (!!int)::3\n",
 		},
 	},
+	{
+		description: "null length",
+		document:    `{a: null}`,
+		expression:  `.a | length`,
+		expected: []string{
+			"D0, P[a], (!!int)::0\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{a: ~}`,
+		expression: `.a | length`,
+		expected: []string{
+			"D0, P[a], (!!int)::0\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{a: key no exist}`,
+		expression: `.b | length`,
+		expected: []string{
+			"D0, P[b], (!!int)::0\n",
+		},
+	},
 	{
 		description:    "Map length",
 		subdescription: "returns number of entries",