Cant show plot on a graph matlab GUI

the plot for the graph dont appear when i input the values

            %Reading Value for selected signal Converter
            selectedFunction = app.DropDown.Value;
            
            Fs = 1000;      % Sampling frequency (Hz)
            T = 1/Fs;       % Sampling period (seconds)
            L = 1000;       % Length of signal (number of samples)
            t = (0:L-1)*T;  % Time vector

            %Reading input parameter
            f1 = str2double(app.Frequency1EditField.Value);
            f2 = str2double(app.Frequency2EditField.Value);
            
            %Initialize Signal
            x = [];

            %Selecting function
            switch selectedFunction
                case "Fourier"
               
                    x = sin(2*pi*f1*t) + sin(2*pi*f2*t);
                    % Add noise if the checkbox is selected (i.e., checked)
                    if app.WhiteNoiseRemoverCheckBox.Value
                        x = x + 0.5 * randn(size(t)); % Add noise when checkbox is checked
                    end
                    y = fft(x);
                    % Compute the two-sided spectrum
                    P2 = abs(y/L);    % Magnitude of the FFT divided by the length
                    P1 = P2(1:L/2+1); % Single-sided spectrum (positive frequencies)
                    P1(2:end-1) = 2*P1(2:end-1); % Adjust for the single-sided spectrum
                    
                    % Define the frequency axis
                    f = Fs*(0:(L/2))/L;
                    
                    plot(app.UIAxes, t, x);
                    plot(app.UIAxes_2, f, P1);

Answer 1

[Walter Roberson]

            selectedFunction = app.DropDown.Value;

That is going to reply with a character vector even if the Items was initialized with a string array. uidropdown() converts string arrays into cell array of character vectors.