[FIX] Resource: getStream for empty string (#249)

When a Resource is created parameter `string` can be passed.
For an empty string `""` calling Resource#getStream
threw an error:  `Resource ${this._path} has no content`

Now the empty string is properly set and the stream can be retrieved.

lib/Resource.js

@@ -73,7 +73,7 @@ class Resource {
  this._createStream = createStream || null;
  this._stream = stream || null;
  this._buffer = buffer || null;
- if (string) {
+ if (typeof string === "string" || string instanceof String) {
  this._buffer = Buffer.from(string, "utf8");
  }
 

test/lib/Resource.js

@@ -18,6 +18,27 @@ function createBasicResource() {
  return resource;
 }
 
+/**
+ * Reads a readable stream and resolves with its content
+ *
+ * @param {stream.Readable} readableStream readable stream
+ * @returns {Promise<string>} resolves with the read string
+ */
+const readStream = (readableStream) => {
+ return new Promise((resolve, reject) => {
+ let streamedResult = "";
+ readableStream.on("data", (chunk) => {
+ streamedResult += chunk;
+ });
+ readableStream.on("end", () => {
+ resolve(streamedResult);
+ });
+ readableStream.on("error", (err) => {
+ reject(err);
+ });
+ });
+};
+
 test("Resource: constructor with missing path parameter", (t) => {
  t.throws(() => {
  new Resource({});
@@ -62,20 +83,38 @@ test("Resource: getStream", async (t) => {
  buffer: Buffer.from("Content")
  });
 
- return new Promise(function(resolve, reject) {
- let streamedResult = "";
- const readableStream = resource.getStream();
- readableStream.on("data", (chunk) => {
- streamedResult += chunk;
- });
- readableStream.on("end", () => {
- resolve(streamedResult);
- });
- }).then((result) => {
+ return readStream(resource.getStream()).then((result) => {
  t.is(result, "Content", "Stream has been read correctly");
  });
 });
 
+test("Resource: getStream for empty string", async (t) => {
+ t.plan(1);
+
+ const resource = new Resource({
+ path: "my/path/to/resource",
+ string: ""
+ });
+
+ return readStream(resource.getStream()).then((result) => {
+ t.is(result, "", "Stream has been read correctly for empty string");
+ });
+});
+
+test("Resource: getStream for empty string instance", async (t) => {
+ t.plan(1);
+
+ const resource = new Resource({
+ path: "my/path/to/resource",
+ // eslint-disable-next-line no-new-wrappers
+ string: new String("")
+ });
+
+ return readStream(resource.getStream()).then((result) => {
+ t.is(result, "", "Stream has been read correctly for empty string");
+ });
+});
+
 test("Resource: getStream throwing an error", (t) => {
  const resource = new Resource({
  path: "my/path/to/resource"