title: Fetch only keys from JSON Object using groovy
body: <p>This is my JSON Object</p>
  
  <pre><code>{
  "master": {
     "node": "xyz", 
     "files": [{"type": "modified", "file": "test.txt"}]
     }, 
  "testbranch2": {
     "node": "abc", 
     "files": [{"type": "modified", "file": "test.txt"}] 
     }, 
  "testbranch": {
     "node": "xxx", 
     "files": [{"type": "modified", "file": "test.txt"}], 
     }
  }
  </code></pre>
  
  <p>I need only the object key names, like "master", "testbranch2","testbranch. How do I fetch only the object key names using groovy?</p>