ES error on task creation

<div style="border:1px solid #990000;padding-left:20px;margin:0 0 10px 0;">

<h4>A PHP Error was encountered</h4>

<p>Severity: Notice</p>
<p>Message:  Undefined index: [1, 2, 3, 4]</p>
<p>Filename: libraries/ElasticSearch.php</p>
<p>Line Number: 894</p>


	<p>Backtrace:</p>
	
		
	
		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/libraries/ElasticSearch.php<br />
			Line: 894<br />
			Function: _error_handler			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/libraries/ElasticSearch.php<br />
			Line: 850<br />
			Function: build_task			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/libraries/ElasticSearch.php<br />
			Line: 319<br />
			Function: index_task			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/models/api/v1/Api_task.php<br />
			Line: 401<br />
			Function: index			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/models/api/v1/Api_task.php<br />
			Line: 47<br />
			Function: task_upload			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/controllers/Api_new.php<br />
			Line: 166<br />
			Function: bootstrap			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/controllers/Api_new.php<br />
			Line: 121<br />
			Function: bootstrap			</p>

		
	
		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/index.php<br />
			Line: 334<br />
			Function: require_once			</p>

		
	

</div>
<div style="border:1px solid #990000;padding-left:20px;margin:0 0 10px 0;">

<h4>A PHP Error was encountered</h4>

<p>Severity: Notice</p>
<p>Message:  Undefined index: [1, 2, 3, 4]</p>
<p>Filename: libraries/ElasticSearch.php</p>
<p>Line Number: 898</p>


	<p>Backtrace:</p>
	
		
	
		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/libraries/ElasticSearch.php<br />
			Line: 898<br />
			Function: _error_handler			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/libraries/ElasticSearch.php<br />
			Line: 850<br />
			Function: build_task			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/libraries/ElasticSearch.php<br />
			Line: 319<br />
			Function: index_task			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/models/api/v1/Api_task.php<br />
			Line: 401<br />
			Function: index			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/models/api/v1/Api_task.php<br />
			Line: 47<br />
			Function: task_upload			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/controllers/Api_new.php<br />
			Line: 166<br />
			Function: bootstrap			</p>

		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/openml_OS/controllers/Api_new.php<br />
			Line: 121<br />
			Function: bootstrap			</p>

		
	
		
	
		
			<p style="margin-left:10px">
			File: /var/www/openml.org/public_html/index.php<br />
			Line: 334<br />
			Function: require_once			</p>