fix(stringToParts): handle empty string and trailing dot the same way that split() does for backwards compat

Re: Automattic/mongoose#9681

Author: vkarpov15

lib/stringToParts.js

@@ -25,9 +25,7 @@ module.exports = function stringToParts(str) {
       curPropertyName += str[i];
     }
   }
-  if (curPropertyName.length > 0) {
-    result.push(curPropertyName);
-  }
+  result.push(curPropertyName);
 
   return result;
 };

test/stringToParts.js

@@ -17,4 +17,12 @@ describe('stringToParts', function() {
   it('throws for invalid numbers in square brackets', function() {
     assert.throws(() => stringToParts('foo[1mystring]'), /1mystring/);
   });
+
+  it('handles empty string', function() {
+    assert.deepEqual(stringToParts(''), ['']);
+  });
+
+  it('handles trailing dot', function() {
+    assert.deepEqual(stringToParts('a.b.'), ['a', 'b', '']);
+  });
 });