InkForge/app/InkForge.Desktop/Views/Tools/WorkspaceTool.axaml

<UserControl xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:local="using:InkForge.Desktop.Views.Tools"
             xmlns:workspaces="using:InkForge.Desktop.Views.Workspaces"
             xmlns:vm="using:InkForge.Desktop.ViewModels.Tools"
             mc:Ignorable="d"
             d:DesignWidth="800"
             d:DesignHeight="450"
             x:Class="InkForge.Desktop.Views.Tools.WorkspaceTool"
             x:DataType="vm:WorkspaceTool"
             Classes.HasWorkspace="{CompiledBinding Workspace, Converter={x:Static ObjectConverters.IsNotNull}}">

  <UserControl.Styles>
    <Style Selector="local|WorkspaceTool">
      <Setter Property="Content">
        <Template>
          <TextBlock>No workspace selected.</TextBlock>
        </Template>
      </Setter>

      <Style Selector="^.HasWorkspace">
        <Setter Property="Content">
          <Template>
            <workspaces:WorkspaceView DataContext="{CompiledBinding Workspace}" />
          </Template>
        </Setter>
      </Style>
    </Style>
  </UserControl.Styles>
</UserControl>