setCopy[k] = v
	}
	return setCopy
}

// add - adds TargetID to the set.
func (set TargetIDSet) add(targetID TargetID) {
	set[targetID] = struct{}{}
}

// Union - returns union with given set as new set.
func (set TargetIDSet) Union(sset TargetIDSet) TargetIDSet {
	nset := set.Clone()

	for k := range sset {
		nset.add(k)
	}

	return nset
}

```

////

The query parameter `q` is of type `Union[str, None]` (or `str | None` in Python 3.10), that means that it's of type `str` but could also be `None`, and indeed, the default value is `None`, so FastAPI will know it's not required.

/// note

FastAPI will know that the value of `q` is not required because of the default value `= None`.

        int start = bufferIndex;

        // Read total allocation units.
        this.alloc = SMBUtil.readInt8(buffer, bufferIndex);
        bufferIndex += 8;

        // read caller available allocation units
        this.free = SMBUtil.readInt8(buffer, bufferIndex);
        bufferIndex += 8;

        // skip actual free units
        bufferIndex += 8;

from typing import Union

from fastapi import Depends, FastAPI

app = FastAPI()


fake_items_db = [{"item_name": "Foo"}, {"item_name": "Bar"}, {"item_name": "Baz"}]


class CommonQueryParams:
    def __init__(self, q: Union[str, None] = None, skip: int = 0, limit: int = 100):
        self.q = q
        self.skip = skip
        self.limit = limit


@app.get("/items/")
async def read_items(commons=Depends(CommonQueryParams)):

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        Union[str, None],
        Query(
            alias="item-query",
            title="Query string",
            description="Query string for the items to search in the database that have a good match",
            min_length=3,

from typing import Annotated, Union

from fastapi import Depends, FastAPI

app = FastAPI()


fake_items_db = [{"item_name": "Foo"}, {"item_name": "Bar"}, {"item_name": "Baz"}]


class CommonQueryParams:
    def __init__(self, q: Union[str, None] = None, skip: int = 0, limit: int = 100):
        self.q = q
        self.skip = skip
        self.limit = limit


@app.get("/items/")

from typing import Annotated, Any, Union

from fastapi import Depends, FastAPI

app = FastAPI()


fake_items_db = [{"item_name": "Foo"}, {"item_name": "Bar"}, {"item_name": "Baz"}]


class CommonQueryParams:
    def __init__(self, q: Union[str, None] = None, skip: int = 0, limit: int = 100):
        self.q = q
        self.skip = skip
        self.limit = limit


@app.get("/items/")

from typing import Union


def process_item(item: Union[int, str]):

from dataclasses import field  # (1)
from typing import List, Union

from fastapi import FastAPI
from pydantic.dataclasses import dataclass  # (2)


@dataclass
class Item:
    name: str
    description: Union[str, None] = None


@dataclass
class Author:
    name: str
    items: List[Item] = field(default_factory=list)  # (3)


app = FastAPI()

from typing import Union

from fastapi import BackgroundTasks, Depends, FastAPI

app = FastAPI()


def write_log(message: str):
    with open("log.txt", mode="a") as log:
        log.write(message)


def get_query(background_tasks: BackgroundTasks, q: Union[str, None] = None):
    if q:
        message = f"found query: {q}\n"
        background_tasks.add_task(write_log, message)
    return q