fix: add package.json/npm-shrinkwrap.json only if they exists

Author: pvdlg

lib/publish.js

@@ -1,4 +1,4 @@
-const {readFile, writeFile, ensureFile} = require('fs-extra');
+const {readFile, writeFile, ensureFile, pathExists} = require('fs-extra');
 const {isUndefined, isPlainObject, isArray} = require('lodash');
 const {template, castArray, uniq} = require('lodash');
 const micromatch = require('micromatch');
@@ -54,9 +54,11 @@ module.exports = async (pluginConfig, {branch, repositoryUrl}, lastRelease, next
 
   const modifiedFiles = await getModifiedFiles();
 
-  if (isUndefined(assets)) {
+  if (isUndefined(assets) && (await pathExists(PKG_JSON))) {
     logger.log('Add %s to the release commit', PKG_JSON);
     patterns.push(PKG_JSON);
+  }
+  if (isUndefined(assets) && (await pathExists(SKW_JSON))) {
     logger.log('Add %s to the release commit', SKW_JSON);
     patterns.push(SKW_JSON);
   }