php-fhir: TypeError : strlen(): Argument #1 ($string) must be of type string, bool given in FHIRTiming

I am getting the following error TypeError : strlen(): Argument #1 ($string) must be of type string, bool given when trying to parse a FHIRTiming object with the following input data:

<timing>
  <repeat>
     <frequency value="1"/>
     <period value="1"/>
     <periodUnit value="d"/>
  </repeat>
</timing>

The error is caused by a check if there are decimals. When there are no decimals strstr will return false and strlen(false) will produce this error.

https://github.com/dcarbone/php-fhir/blob/master/template/properties/methods/primitive/decimal_type.php#L39

Besides that is frequency of type PositiveInt so a decimal should not be accepted.