How can I run the filter function only when the searchbar text is not empty?

I have a search button and a search bar in SwiftUi View. i'm try to run the function filter() when the user type in the Searchbar.

If I use the button to trig the action it works, but I want to trig the action when user typing in the bar.

I have tried with if else but give me a warning.

Generic parameter 'FalseContent' could not be inferred 1. In call to function 'buildEither(first:)' (SwiftUI.ViewBuilder)

here my code

struct ContentView: View {
    @ObservedObject var dm: DataManager
    @State private var searchTerm : String = ""
    @State var filteredAirports: [AirportModel] = []

    var body: some View {
        VStack {
            SearchBar(text: $searchTerm)
            if searchTerm == "" {
                /// don't do anything 
            } else {
                self.dm.filter2(valoreSearhed: self.searchTerm, arrayTosearh: self.dm.airportVector)
            }

            List {
                ForEach(dm.appoggio) { valore in
                    Text(valore.aptICAO)
                }
            }
        }
    }
}
``