Fix error message selection condition (#3037)

I have no idea how this eluded me when I first wrote this. Also, add tests to make sure the check was correct from the beginning.

Author: dead-claudia

render/tests/test-normalizeChildren.js

@@ -53,4 +53,68 @@ o.spec("normalizeChildren", function() {
 			])
 		}).throws(TypeError)
 	})
+	o("disallows mixed keys, ending with null", function() {
+		o(function() {
+			Vnode.normalizeChildren([
+				{key: 1},
+				null,
+			])
+		}).throws(TypeError)
+	})
+	o("disallows mixed keys, starting with null", function() {
+		o(function() {
+			Vnode.normalizeChildren([
+				{data: 1},
+				null,
+			])
+		}).throws(TypeError)
+	})
+	o("disallows mixed keys, ending with undefined", function() {
+		o(function() {
+			Vnode.normalizeChildren([
+				{key: 1},
+				undefined,
+			])
+		}).throws(TypeError)
+	})
+	o("disallows mixed keys, starting with undefined", function() {
+		o(function() {
+			Vnode.normalizeChildren([
+				{data: 1},
+				undefined,
+			])
+		}).throws(TypeError)
+	})
+	o("disallows mixed keys, ending with false", function() {
+		o(function() {
+			Vnode.normalizeChildren([
+				{key: 1},
+				false,
+			])
+		}).throws(TypeError)
+	})
+	o("disallows mixed keys, starting with false", function() {
+		o(function() {
+			Vnode.normalizeChildren([
+				{data: 1},
+				false,
+			])
+		}).throws(TypeError)
+	})
+	o("disallows mixed keys, ending with true", function() {
+		o(function() {
+			Vnode.normalizeChildren([
+				{key: 1},
+				true,
+			])
+		}).throws(TypeError)
+	})
+	o("disallows mixed keys, starting with true", function() {
+		o(function() {
+			Vnode.normalizeChildren([
+				{data: 1},
+				true,
+			])
+		}).throws(TypeError)
+	})
 })

render/vnode.js

@@ -19,7 +19,7 @@ Vnode.normalizeChildren = function(input) {
 		for (var i = 1; i < input.length; i++) {
 			if ((input[i] != null && input[i].key != null) !== isKeyed) {
 				throw new TypeError(
-					isKeyed && (input[i] != null || typeof input[i] === "boolean")
+					isKeyed && (input[i] == null || typeof input[i] === "boolean")
 						? "In fragments, vnodes must either all have keys or none have keys. You may wish to consider using an explicit keyed empty fragment, m.fragment({key: ...}), instead of a hole."
 						: "In fragments, vnodes must either all have keys or none have keys."
 				)