title: JHipster export-jdl problems
body: <p>I have a test project.
  I have deleted by mistake jdl file.
  Now, when i try to recreate jdl file from existing project using</p>
  
  <pre><code>jhipster export-jdl
  </code></pre>
  
  <p>i receive this message:</p>
  
  <pre><code>Using JHipster version installed locally in current project's node_modules
  Executing jhipster:export-jdl
  Options: 
  Parsing entities from .jhipster dir...
  The passed validation must be valid.
  Errors: No value
  events.js:183
    throw er; // Unhandled 'error' event
    ^
  
  Error: ERROR! 
  Error while parsing entities to JDL
  
  at Environment.error (/home/igor/Development/IdeaProjects/StoVehiclesManagementSystems/node_modules/generator-jhipster/node_modules/yeoman-environment/lib/environment.js:157:40)
  at module.exports.error (/home/igor/Development/IdeaProjects/StoVehiclesManagementSystems/node_modules/generator-jhipster/generators/generator-base.js:2048:18)
  at module.exports.generateJDLFromEntities (/home/igor/Development/IdeaProjects/StoVehiclesManagementSystems/node_modules/generator-jhipster/generators/generator-base-private.js:1002:18)
  at module.exports.parseJson (/home/igor/Development/IdeaProjects/StoVehiclesManagementSystems/node_modules/generator-jhipster/generators/export-jdl/index.js:39:33)
  at Object.&lt;anonymous&gt; (/home/igor/Development/IdeaProjects/StoVehiclesManagementSystems/node_modules/yeoman-generator/lib/index.js:418:27)
  at /home/igor/Development/IdeaProjects/StoVehiclesManagementSystems/node_modules/run-async/index.js:25:25
  at new Promise (&lt;anonymous&gt;)
  at /home/igor/Development/IdeaProjects/StoVehiclesManagementSystems/node_modules/run-async/index.js:24:19
  at self.env.runLoop.add.completed (/home/igor/Development/IdeaProjects/StoVehiclesManagementSystems/node_modules/yeoman-generator/lib/index.js:419:13)
  at runCallback (timers.js:810:20)
  </code></pre>
  
  <p>Any idea what could be a problem?</p>