Got FEEL/SCALA-01008 when inputExpression is 'function' on 7.13.0

<dmn:input id="_83CB7098-E65E-4CD8-B8AA-5991D23BAEA2">
    <dmn:inputExpression id="_B67DF868-5121-40F6-9308-5E4C4584EDA2" typeRef="string">
        <dmn:text>function</dmn:text>
    </dmn:inputExpression>
</dmn:input>

Exception in thread "main" org.camunda.bpm.dmn.feel.impl.FeelException: FEEL/SCALA-01008 Error while evaluating expression: failed to parse expression 'function': [1.9] error: '(' expected but end of source found

function
        ^
	at org.camunda.bpm.dmn.feel.impl.scala.ScalaFeelLogger.evaluationException(ScalaFeelLogger.java:77)
	at org.camunda.bpm.dmn.feel.impl.scala.ScalaFeelEngine.evaluateSimpleExpression(ScalaFeelEngine.java:82)
	at org.camunda.bpm.dmn.engine.impl.evaluation.ExpressionEvaluationHandler.evaluateFeelSimpleExpression(ExpressionEvaluationHandler.java:130)
	at org.camunda.bpm.dmn.engine.impl.evaluation.ExpressionEvaluationHandler.evaluateExpression(ExpressionEvaluationHandler.java:59)
	at org.camunda.bpm.dmn.engine.impl.evaluation.DecisionTableEvaluationHandler.evaluateInputExpression(DecisionTableEvaluationHandler.java:193)
	at org.camunda.bpm.dmn.engine.impl.evaluation.DecisionTableEvaluationHandler.evaluateInput(DecisionTableEvaluationHandler.java:122)
	at org.camunda.bpm.dmn.engine.impl.evaluation.DecisionTableEvaluationHandler.evaluateDecisionTable(DecisionTableEvaluationHandler.java:104)
	at org.camunda.bpm.dmn.engine.impl.evaluation.DecisionTableEvaluationHandler.evaluate(DecisionTableEvaluationHandler.java:81)
	at org.camunda.bpm.dmn.engine.impl.DefaultDmnDecisionContext.evaluateDecision(DefaultDmnDecisionContext.java:85)
	at org.camunda.bpm.dmn.engine.impl.DefaultDmnEngine.evaluateDecisionTable(DefaultDmnEngine.java:115)
	at org.camunda.bpm.dmn.engine.impl.DefaultDmnEngine.evaluateDecisionTable(DefaultDmnEngine.java:105)
	at com.example.dmntest.Main.main(Main.java:23)