Answered getCollectionGraph - Fatal error: Call to a member function get() on a non-object

$criteria = $modx->newQuery('Tutor');
$thecharts = $modx->getCollectionGraph('Tutor', '{"TutorToPupil":{} }', $criteria);
foreach ($thecharts as $thechart) {
    $tutor = $thechart->get('id');
	$pupil = $thechart->TutorToPupil->get('tutor_id');
	//$chart = $thechart->PupilTochart->get('pupil_id');
	$output .= '<p>';
	$output .= $tutor .' - ' . $pupil;// .' - ' . $chart;
	$output .= '</p>';

}

<?xml version="1.0" encoding="UTF-8"?>
<model package="sohow" baseClass="xPDOObject" platform="mysql" defaultEngine="MyISAM" version="1.1">
	<object class="Chart" table="chart" extends="xPDOSimpleObject">
		<field key="pupil_id" dbtype="int" precision="11" phptype="integer" null="false" index="index" />

		<index alias="pupil_id" name="pupil_id" primary="false" unique="false" type="BTREE" >
			<column key="pupil_id" length="" collation="A" null="false" />
		</index>
		<composite alias="ChartToFeeling" class="Feeling" local="id" foreign="chart_id" cardinality="many" owner="local" />
		<aggregate alias="ChartFromPupil" class="Pupil" local="pupil_id" foreign="id" cardinality="one" owner="foreign" />

	</object>
	<object class="Feeling" table="feeling" extends="xPDOSimpleObject">
		<field key="chart_id" dbtype="int" precision="11" phptype="integer" null="false" index="index" />

		<index alias="chart_id" name="chart_id" primary="false" unique="false" type="BTREE" >
			<column key="chart_id" length="" collation="A" null="false" />
		</index>
		<aggregate alias="FeelingFromChart" class="Chart" local="chart_id" foreign="id" cardinality="one" owner="foreign" />
	</object>
	<object class="Pupil" table="pupil" extends="xPDOSimpleObject">
		<field key="tutor_id" dbtype="int" precision="11" phptype="integer" null="false" index="index" />

		<index alias="tutor_id" name="tutor_id" primary="false" unique="false" type="BTREE" >
			<column key="tutor_id" length="" collation="A" null="false" />
		</index>
		<aggregate alias="PupilFromTutor" class="Tutor" local="tutor_id" foreign="id" cardinality="one" owner="foreign" />
		<composite alias="PupilToChart" class="Chart" local="id" foreign="pupil_id" cardinality="many" owner="local" />
	</object>
	<object class="Tutor" table="tutor" extends="xPDOSimpleObject">
		<field key="tutor_name" dbtype="varchar" precision="50" phptype="string" null="false" index="index" />

		<index alias="tutor_name" name="tutor_name" primary="false" unique="false" type="BTREE" >
			<column key="tutor_name" length="" collation="A" null="false" />
		</index>
		<composite alias="TutorToPupil" class="Pupil" local="id" foreign="tutor_id" cardinality="many" owner="local" />
	</object>
</model>