Can add and merge append to null

pkg/yqlib/doc/Add.md

@@ -209,3 +209,15 @@ will output
 a: 4
 ```
 
+## Add to null
+Adding to null simply returns the rhs
+
+Running
+```bash
+yq eval --null-input 'null + "cat"'
+```
+will output
+```yaml
+cat
+```
+

pkg/yqlib/operator_add.go

@@ -47,9 +47,14 @@ func add(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*Candida
 	lhs.Node = unwrapDoc(lhs.Node)
 	rhs.Node = unwrapDoc(rhs.Node)
 
-	target := lhs.CreateChild(nil, &yaml.Node{})
 	lhsNode := lhs.Node
 
+	if lhsNode.Tag == "!!null" {
+		return lhs.CreateChild(nil, rhs.Node), nil
+	}
+
+	target := lhs.CreateChild(nil, &yaml.Node{})
+
 	switch lhsNode.Kind {
 	case yaml.MappingNode:
 		return nil, fmt.Errorf("Maps not yet supported for addition")

pkg/yqlib/operator_add_test.go

@@ -112,6 +112,14 @@ var addOperatorScenarios = []expressionScenario{
 			"D0, P[], (doc)::{a: 4}\n",
 		},
 	},
+	{
+		description:    "Add to null",
+		subdescription: "Adding to null simply returns the rhs",
+		expression:     `null + "cat"`,
+		expected: []string{
+			"D0, P[], (!!str)::cat\n",
+		},
+	},
 }
 
 func TestAddOperatorScenarios(t *testing.T) {

pkg/yqlib/operator_multiply_test.go

@@ -144,6 +144,14 @@ b:
 			"D0, P[a], (!!seq)::[{thing: two}]\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		document:   `{a: {array: [1]}, b: {}}`,
+		expression: `.b *+ .a`,
+		expected: []string{
+			"D0, P[b], (!!map)::{array: [1]}\n",
+		},
+	},
 	{
 		description: "Merge, appending arrays",
 		document:    `{a: {array: [1, 2, animal: dog], value: coconut}, b: {array: [3, 4, animal: cat], value: banana}}`,