SBMLToolkit currently enforces stoich to be non-zero

s1 -> s1

<?xml version="1.0" encoding="UTF-8"?>
<!-- Created by COPASI version 4.30 (Build 240) on 2021-07-26 16:51 with libSBML version 5.19.0. -->
<sbml xmlns="http://www.sbml.org/sbml/level2/version4" level="2" version="4">
  <model metaid="COPASI0" id="prod_subtrate_same" name="prod_subtrate_same">
    <listOfUnitDefinitions>
      <unitDefinition id="substance" name="substance">
        <listOfUnits>
          <unit kind="mole" exponent="1" scale="0" multiplier="1"/>
        </listOfUnits>
      </unitDefinition>
      <unitDefinition id="length" name="length">
        <listOfUnits>
          <unit kind="metre" exponent="1" scale="0" multiplier="1"/>
        </listOfUnits>
      </unitDefinition>
      <unitDefinition id="area" name="area">
        <listOfUnits>
          <unit kind="metre" exponent="2" scale="0" multiplier="1"/>
        </listOfUnits>
      </unitDefinition>
      <unitDefinition id="volume" name="volume">
        <listOfUnits>
          <unit kind="litre" exponent="1" scale="0" multiplier="1"/>
        </listOfUnits>
      </unitDefinition>
      <unitDefinition id="time" name="time">
        <listOfUnits>
          <unit kind="second" exponent="1" scale="0" multiplier="1"/>
        </listOfUnits>
      </unitDefinition>
    </listOfUnitDefinitions>
    <listOfCompartments>
      <compartment metaid="COPASI1" id="compartment" name="compartment" spatialDimensions="3" size="1" constant="true">
      </compartment>
    </listOfCompartments>
    <listOfSpecies>
      <species metaid="COPASI3" id="s1" name="s1" compartment="compartment" initialConcentration="1" boundaryCondition="false" constant="false">
      </species>
    </listOfSpecies>
    <listOfReactions>
      <reaction metaid="COPASI4" id="reaction" name="reaction" reversible="false">
        <listOfReactants>
          <speciesReference species="s1"/>
        </listOfReactants>
        <listOfProducts>
          <speciesReference species="s1"/>
        </listOfProducts>
        <kineticLaw>
          <math xmlns="http://www.w3.org/1998/Math/MathML">
            <apply>
              <times/>
              <ci> compartment </ci>
              <ci> k1 </ci>
              <ci> s1 </ci>
            </apply>
          </math>
          <listOfParameters>
            <parameter id="k1" name="k1" value="0.1"/>
          </listOfParameters>
        </kineticLaw>
      </reaction>
    </listOfReactions>
  </model>
</sbml>