@user_router.get("/{user_id}")
def get_user(user_id: str):
    return {"user_id": user_id}


@item_router.get("/")
def get_items(user_id: Optional[str] = None):
    if user_id is None:
        return [{"item_id": "i1", "user_id": "u1"}, {"item_id": "i2", "user_id": "u2"}]
    else:
        return [{"item_id": "i2", "user_id": user_id}]


@item_router.get("/{item_id}")
def get_item(item_id: str, user_id: Optional[str] = None):

a select with only <code>nil</code> channels and no default case blocks forever.
</p>

<pre>
var a []int
var c, c1, c2, c3, c4 chan int
var i1, i2 int
select {
case i1 = &lt;-c1:
	print("received ", i1, " from c1\n")
case c2 &lt;- i2:
	print("sent ", i2, " to c2\n")
case i3, ok := (&lt;-c3):  // same as: i3, ok := &lt;-c3
	if ok {
		print("received ", i3, " from c3\n")

SHA512SU1 V5.D2, in2.D2, in0.D2 \ VADD i3.D2, i1.D2, i4.D2 \ SHA512H2 i0.D2, i1, i3 #define SHA512ROUND_NO_UPDATE(i0, i1, i2, i3, i4, rc0, rc1, in0) \ VLD1.P 16(R4), [rc1.D2] \ SHA512TRANS(i0, i1, i2, i3, i4, rc0, in0) \ SHA512H V7.D2, V6, i3 \ VADD i3.D2, i1.D2, i4.D2 \ SHA512H2 i0.D2, i1, i3 #define SHA512ROUND_LAST(i0, i1, i2, i3, i4, rc0, in0) \ SHA512TRANS(i0, i1, i2, i3, i4, rc0, in0) \ SHA512H V7.D2, V6, i3 \ VADD i3.D2, i1.D2, i4.D2 \ SHA512H2 i0.D2, i1, i3 // func blockSHA512(dig *Digest, p []byte)...