code: protected void setErrorMessageVariableOnErrorEventDefinition(Element errorEventDefinition, ErrorEventDefinition definition) {
      String errorMessageVariable = errorEventDefinition.attributeNS(CAMUNDA_BPMN_EXTENSIONS_NS, "errorMessageVariable");
      if (errorMessageVariable != null) {
        definition.setErrorMessageVariable(errorMessageVariable);
      }
    }
docs: Sets the value for "camunda:errorMessageVariable" on the passed definition if
  it's present.
  
  @param errorEventDefinition
  the XML errorEventDefinition tag
  @param definition
  the errorEventDefintion that can get the errorMessageVariable value