feat: 🎸 check for staged files

lib/cli.js

@@ -1,4 +1,4 @@
-const {spawn} = require('child_process');
+const {spawn, execSync} = require('child_process');
 const fs = require('fs');
 const {join} = require('path');
 const shellescape = require('any-shell-escape');
@@ -27,6 +27,20 @@ const executeCommand = (command, args = [], env = process.env) => {
 
 const main = async () => {
   try {
+    try {
+      /**
+       * @author https://github.com/rodrigograca31
+       * @see https://github.com/streamich/git-cz/issues/177
+       *
+       * It exits with 1 if there were differences and 0 means no differences.
+       * Because of that we negate it to only throw an error if there's no files staged
+       * https://stackoverflow.com/questions/367069/how-can-i-negate-the-return-value-of-a-process
+       */
+      execSync('! git diff HEAD --staged --quiet --exit-code');
+    } catch (error) {
+      throw new Error('No files staged.');
+    }
+
     const {cliAnswers, cliOptions, passThroughParams} = parseArgs();
 
     if (cliOptions.dryRun) {