Chain of responsibility pattern rookie attempt

I'm trying to find understanding of Chain of responsibility pattern, and, as an exercise, I've wrote some code. This code

class SomeObject:
    def __init__(self):
        self.integer_field = 0
        self.float_field = 0.0
        self.string_field = 'hi'


class EventGet:
    def __init__(self, data_type):
        self.data_type = data_type

class EventSet:
    def __init__(self, value):
        self.value = value


class NullHandler:
    def __init__(self, successor=None):
        self.__successor = successor

    def handle(self, obj, event):
        if self.__successor:
            self.__successor.handle(obj, event)


class IntHandler(NullHandler):
    def handle(self, obj, event):
        if isinstance(event, EventGet) and event.data_type is int:
            return obj.integer_field
        elif isinstance(event, EventSet) and isinstance(event.value, int):
            obj.integer_field = event.value
        else:
            super().handle(obj, event)


class FloatHandler(NullHandler):
    def handle(self, obj, event):
        if isinstance(event, EventGet) and event.data_type is float:
            return obj.float_field
        elif isinstance(event, EventSet) and isinstance(event.value, float):
            obj.float_field = event.value
        else:
            super().handle(obj, event)


class StrHandler(NullHandler):
    def handle(self, obj, event):
        if isinstance(event, EventGet) and event.data_type is str:
            return obj.string_field
        elif isinstance(event, EventSet) and isinstance(event.value, str):
            obj.string_field = event.value
        else:
            super().handle(obj, event)

But it doesn't work as I'm expecting. Being invoked in the following manner

obj = SomeObject()
chain = IntHandler(FloatHandler(StrHandler(NullHandler())))

print(chain.handle(obj, EventGet(int)))
print(chain.handle(obj, EventGet(float)))
print(chain.handle(obj, EventGet(str)))

chain.handle(obj, EventSet(1))
print(obj.integer_field)    

chain.handle(obj, EventSet(1.1))
print(obj.float_field)

chain.handle(obj, EventSet('str'))
print(obj.string_field)

it produces the confusing output:

0 # That's ok
None # Why not 0.0?
None # Why not hi?
1 # That's ok
1.1 # That's ok
str # That's ok

I can't figure out why calling the chain.handle(obj, EventGet(float)) and chain.handle(obj, EventGet(str)) produces None. After all, there's a return statement in corresponding positions (i.e. return obj.float_field and return obj.string_field).

Can you please explain to me what is wrong in this code and how to make it work as expected? Many thanks in advance!