ESLint: expected to assign or call a function and saw an expression instead. (No-unused-expressions)?

Question

Linter

public stop (): void {
    this._processConnectingAndDisconnecting = true
    this._ua?.stop()
    this._ua?.unregister({ all: true })
 }

this._ua?.stop()Equivalent to this this._uaif this._ua == null|undefined

linter swears

ESLint: Expected an assignment or function call and instead saw an expression.(no-unused-expressions)

That is, the property is allegedly not assigned anywhere, which is quite logical.
How to proceed?

Should I ignore this message?