get_related_instances does not work with boolean parameters

[zyko]

A task A, that has bool parameters cannot be found with A.get_related_instances() as shown in the following example:

import os
import luisy
import luigi

class MyAbstractClass(luisy.Task):
    def run(self):
        self.write(str("test"))

class MyBoolTask(MyAbstractClass):
    test_boolean = luisy.BoolParameter(False)

class MyIntTask(MyAbstractClass):
    test_int = luisy.IntParameter(42)

task1 = MyBoolTask()
task2 = MyIntTask()
luigi.build([task1, task2], local_scheduler=True)


# show that files are created on disk:
for task_file in os.listdir(os.getenv("WORKING_DIR")):
    if "Task" in task_file:
        print(task_file)

assert MyIntTask.get_related_instances()[0].read() == "test"
assert MyBoolTask.get_related_instances()[0].read() == "test"
# this assert fails, because get_related instances doesn't find any files at all.