Use explicit default arguments (#2421)

src/language/printer.js

@@ -255,8 +255,8 @@ function addDescription(cb) {
  * Given maybeArray, print an empty string if it is null or empty, otherwise
  * print all items together separated by separator if provided
  */
-function join(maybeArray, separator) {
-  return maybeArray ? maybeArray.filter(x => x).join(separator || '') : '';
+function join(maybeArray: ?Array<string>, separator = '') {
+  return maybeArray?.filter(x => x).join(separator) || '';
 }
 
 /**
@@ -273,8 +273,8 @@ function block(array) {
  * If maybeString is not null or empty, then wrap with start and end, otherwise
  * print an empty string.
  */
-function wrap(start, maybeString, end) {
-  return maybeString ? start + maybeString + (end || '') : '';
+function wrap(start, maybeString, end = '') {
+  return maybeString ? start + maybeString + end : '';
 }
 
 function indent(maybeString) {

src/language/source.js

@@ -22,10 +22,14 @@ export class Source {
   name: string;
   locationOffset: Location;
 
-  constructor(body: string, name?: string, locationOffset?: Location): void {
+  constructor(
+    body: string,
+    name: string = 'GraphQL request',
+    locationOffset: Location = { line: 1, column: 1 },
+  ): void {
     this.body = body;
-    this.name = name != null ? name : 'GraphQL request';
-    this.locationOffset = locationOffset || { line: 1, column: 1 };
+    this.name = name;
+    this.locationOffset = locationOffset;
     devAssert(
       this.locationOffset.line > 0,
       'line in locationOffset is 1-indexed and must be positive.',