<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def to_source(self, classname):
 """ Returns the model as Java source code if the classifier implements weka.classifiers.Sourcable. :param classname: the classname for the generated Java code :type classname: str :return: the model as source code string :rtype: str """

        if not self.check_type(self.jobject, "weka.classifiers.Sourcable"):
            return None
        return javabridge.call(self.jobject, "toSource", "(Ljava/lang/String;)Ljava/lang/String;", classname)