[Fix] default_stream: do not error on nullish data

altho tape itself would never trigger it, this is an entry point

lib/default_stream.js

@@ -9,6 +9,13 @@ module.exports = function () {
 	return stream;
 
 	function write(buf) {
+		if (
+			buf == null // eslint-disable-line eqeqeq
+			|| (Object(buf) !== buf && typeof buf !== 'string')
+		) {
+			flush();
+			return;
+		}
 		for (var i = 0; i < buf.length; i++) {
 			var c = typeof buf === 'string'
 				? buf.charAt(i)

test/default_stream.js

@@ -0,0 +1,20 @@
+'use strict';
+
+var tap = require('tap');
+
+var getDefaultStream = require('../lib/default_stream');
+
+tap.test('getDefaultStream', function (tt) {
+	tt.plan(5);
+
+	var stream = getDefaultStream();
+
+	tt.doesNotThrow(function () { stream.write('# ok'); }, 'strings are fine');
+	tt.doesNotThrow(function () { stream.write(123); }, 'numbers are fine');
+	tt.doesNotThrow(function () { stream.write(undefined); }, 'undefined is fine');
+	tt.doesNotThrow(function () { stream.write(); }, 'no args is fine');
+	tt.doesNotThrow(function () { stream.write(null); }, 'null is fine');
+	// TODO: figure out why writing to the stream after writing null fails tests
+
+	tt.end();
+});