From f1dbe13f212099b997d77672e64593c078f5c0bb Mon Sep 17 00:00:00 2001
From: Mike Farah <mikefarah@gmail.com>
Date: Tue, 4 Feb 2020 14:21:54 +1100
Subject: [PATCH] Can write and merge into empty files :)

---
 cmd/commands_test.go | 16 ++++++++++++++++
 cmd/utils.go         |  7 ++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/cmd/commands_test.go b/cmd/commands_test.go
index a9d70fdc..62231e44 100644
--- a/cmd/commands_test.go
+++ b/cmd/commands_test.go
@@ -1101,6 +1101,22 @@ func TestWriteCmd(t *testing.T) {
 	test.AssertResult(t, expectedOutput, result.Output)
 }
 
+func TestWriteEmptyCmd(t *testing.T) {
+	content := ``
+	filename := test.WriteTempYamlFile(content)
+	defer test.RemoveTempYamlFile(filename)
+
+	cmd := getRootCommand()
+	result := test.RunCmd(cmd, fmt.Sprintf("write %s b.c 7", filename))
+	if result.Error != nil {
+		t.Error(result.Error)
+	}
+	expectedOutput := `b:
+  c: 7
+`
+	test.AssertResult(t, expectedOutput, result.Output)
+}
+
 func TestWriteCmdScript(t *testing.T) {
 	content := `b:
   c: 3
diff --git a/cmd/utils.go b/cmd/utils.go
index d4e473c4..14e9a9f3 100644
--- a/cmd/utils.go
+++ b/cmd/utils.go
@@ -188,7 +188,12 @@ func mapYamlDecoder(updateData updateDataFn, encoder yqlib.Encoder) yamlDecoderF
 			log.Debugf("Read doc %v", currentIndex)
 			errorReading = decoder.Decode(&dataBucket)
 
-			if errorReading == io.EOF {
+			if errorReading == io.EOF && docIndexInt == 0 && currentIndex == 0 {
+				//empty document, lets just make one
+				child := yaml.Node{Kind: yaml.MappingNode}
+				dataBucket = yaml.Node{Kind: yaml.DocumentNode, Content: make([]*yaml.Node, 1)}
+				dataBucket.Content[0] = &child
+			} else if errorReading == io.EOF {
 				if !updateAll && currentIndex <= docIndexInt {
 					return fmt.Errorf("asked to process document index %v but there are only %v document(s)", docIndex, currentIndex)
 				}