Is it "bad form" to perform map lookup and type assertion in one statement?

I just realized that it's possible to do a map lookup and a type/interface-assertion in one statement.

m := map[string]interface{}{
    "key": "the value",
}
if value, ok := m["key"].(string); ok {
    fmt.Printf("value exists and is a string: %s\n", value)
} else {
    fmt.Println("value does not exist or is not a string")
}

Is this considered bad? I've not seen any official documentation commenting this.

edit: I know this code can not distinguish between "key doesn't exist" and "value is of incorrect type".

edit2: ahem, the print in the else-clause was incorrect :(