When launching `core list` with no installed platforms print `no platforms installed` (#2238)

internal/cli/core/list.go

@@ -82,10 +82,9 @@ func (ir installedResult) Data() interface{} {
 }
 
 func (ir installedResult) String() string {
-	if ir.platforms == nil || len(ir.platforms) == 0 {
-		return ""
+	if len(ir.platforms) == 0 {
+		return tr("No platforms installed.")
 	}
-
 	t := table.New()
 	t.SetHeader(tr("ID"), tr("Installed"), tr("Latest"), tr("Name"))
 	for _, p := range ir.platforms {

internal/integrationtest/core/core_test.go

@@ -1058,3 +1058,16 @@ func TestCoreUpgradeWarningWithPackageInstalledButNotIndexed(t *testing.T) {
 		requirejson.Query(t, jsonStdout, ".warnings[]", `"missing package index for test:x86, future updates cannot be guaranteed"`)
 	})
 }
+
+func TestCoreListWhenNoPlatformAreInstalled(t *testing.T) {
+	env, cli := integrationtest.CreateArduinoCLIWithEnvironment(t)
+	defer env.CleanUp()
+
+	stdout, _, err := cli.Run("core", "list", "--format", "json")
+	require.NoError(t, err)
+	requirejson.Empty(t, stdout)
+
+	stdout, _, err = cli.Run("core", "list")
+	require.NoError(t, err)
+	require.Equal(t, "No platforms installed.\n", string(stdout))
+}