parser: Show empty strings in error messages (#2176)

Author: IvanGoncharov

src/language/__tests__/parser-test.js

@@ -75,6 +75,11 @@ describe('Parser', () => {
       message: 'Syntax Error: Unexpected "...".',
       locations: [{ line: 1, column: 1 }],
     });
+
+    expectSyntaxError('{ ""').to.deep.include({
+      message: 'Syntax Error: Expected Name, found String "".',
+      locations: [{ line: 1, column: 3 }],
+    });
   });
 
   it('parse provides useful error when using source', () => {

src/language/parser.js

@@ -1556,9 +1556,8 @@ defineToJSON(Loc, function() {
  * A helper function to describe a token as a string for debugging
  */
 function getTokenDesc(token: Token): string {
-  return (
-    getTokenKindDesc(token.kind) + (token.value ? ` "${token.value}"` : '')
-  );
+  const value = token.value;
+  return getTokenKindDesc(token.kind) + (value != null ? ` "${value}"` : '');
 }
 
 /**