default_factory and default generated together

[calclavia]

Describe the bug
Follow up on #22

For certain protobufs, this plugin generates a default and a default_factory in Pydantic which causes an error.

To Reproduce
Steps to reproduce the behavior:

syntax = "proto3";

message A {
    optional string a = 2;
    repeated string b = 3;
}

Output:

# This is an automatically generated file, please do not change
# gen by protobuf_to_pydantic[v0.2.0.1](https://github.com/so1n/protobuf_to_pydantic)
# Protobuf Version: 4.24.3
# Pydantic Version: 1.10.12
from google.protobuf.message import Message  # type: ignore
from pydantic import BaseModel
from pydantic import Field
import typing


class A(BaseModel):
    a: typing.Optional[str] = Field(default="")
    b: typing.Optional[typing.List[str]] = Field(default_factory=list, default=None)

Expected behavior
It should only generate the default factory list for repeated and not default=None.