diff --git a/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserActivity.java b/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserActivity.java
index d5a0186b4426..b1c3505aeceb 100644
--- a/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserActivity.java
+++ b/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserActivity.java
@@ -410,7 +410,7 @@ private void fetchInstalledThemesIfJetpackSite() {
         }
     }
 
-    private void activateTheme(String themeId) {
+    private void activateTheme(@NonNull String themeId) {
         if (!mSite.isUsingWpComRestApi()) {
             AppLog.i(T.THEMES, "Theme activation requires a site using WP.com REST API. Aborting request.");
             return;
diff --git a/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserAdapter.java b/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserAdapter.java
index 900feb389b1b..a4d46b6b4198 100644
--- a/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserAdapter.java
+++ b/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserAdapter.java
@@ -170,7 +170,10 @@ public View getView(int position, View convertView, ViewGroup parent) {
     }
 
     @SuppressWarnings("deprecation")
-    private void configureCardView(ThemeViewHolder themeViewHolder, boolean isCurrent) {
+    private void configureCardView(
+            @NonNull ThemeViewHolder themeViewHolder,
+            boolean isCurrent
+    ) {
         if (isCurrent) {
             ColorStateList color = ContextExtensionsKt.getColorStateListFromAttribute(
                     mContext,
@@ -200,10 +203,18 @@ private void configureCardView(ThemeViewHolder themeViewHolder, boolean isCurren
         }
     }
 
-    private void configureImageView(ThemeViewHolder themeViewHolder, String screenshotURL, final String themeId,
-                                    final boolean isCurrent) {
-        mImageManager.load(themeViewHolder.mImageView, ImageType.THEME, getUrlWithWidth(screenshotURL),
-                ScaleType.FIT_CENTER);
+    private void configureImageView(
+            @NonNull ThemeViewHolder themeViewHolder,
+            @NonNull String screenshotURL,
+            @NonNull final String themeId,
+            final boolean isCurrent
+    ) {
+        mImageManager.load(
+                themeViewHolder.mImageView,
+                ImageType.THEME,
+                getUrlWithWidth(screenshotURL),
+                ScaleType.FIT_CENTER
+        );
 
         themeViewHolder.mCardView.setOnClickListener(new View.OnClickListener() {
             @Override
@@ -217,7 +228,8 @@ public void onClick(View v) {
         });
     }
 
-    private String getUrlWithWidth(String screenshotURL) {
+    @NonNull
+    private String getUrlWithWidth(@NonNull String screenshotURL) {
         if (screenshotURL.contains("?")) {
             return screenshotURL + "&" + THEME_IMAGE_PARAMETER + mViewWidth;
         } else {
@@ -225,8 +237,12 @@ private String getUrlWithWidth(String screenshotURL) {
         }
     }
 
-    private void configureImageButton(ThemeViewHolder themeViewHolder, final String themeId, final boolean isPremium,
-                                      boolean isCurrent) {
+    private void configureImageButton(
+            @NonNull ThemeViewHolder themeViewHolder,
+            @NonNull final String themeId,
+            final boolean isPremium,
+            boolean isCurrent
+    ) {
         final PopupMenu popupMenu = new PopupMenu(mContext, themeViewHolder.mImageButton);
         popupMenu.getMenuInflater().inflate(R.menu.theme_more, popupMenu.getMenu());
 
diff --git a/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserFragment.kt b/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserFragment.kt
index 39da031d1bf8..b3fc264ddf07 100644
--- a/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserFragment.kt
+++ b/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeBrowserFragment.kt
@@ -242,7 +242,7 @@ class ThemeBrowserFragment : Fragment(), AbsListView.RecyclerListener,
         }
     }
 
-    fun setCurrentThemeId(currentThemeId: String?) {
+    fun setCurrentThemeId(currentThemeId: String) {
         this.currentThemeId = currentThemeId
         refreshView()
     }
diff --git a/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeWebActivity.java b/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeWebActivity.java
index a8ea5f98baf9..c49fe76d2f01 100644
--- a/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeWebActivity.java
+++ b/WordPress/src/main/java/org/wordpress/android/ui/themes/ThemeWebActivity.java
@@ -54,8 +54,12 @@ public static String getSiteLoginUrl(SiteModel site) {
         return WPWebViewActivity.getSiteLoginUrl(site);
     }
 
-    public static void openTheme(Activity activity, @NonNull SiteModel site, @NonNull ThemeModel theme,
-                                 @NonNull ThemeWebActivityType type) {
+    public static void openTheme(
+            Activity activity,
+            @NonNull SiteModel site,
+            @NonNull ThemeModel theme,
+            @NonNull ThemeWebActivityType type
+    ) {
         String url = getUrl(site, theme, type, !theme.isFree());
         if (TextUtils.isEmpty(url)) {
             ToastUtils.showToast(activity, R.string.could_not_load_theme);
@@ -72,7 +76,12 @@ public static void openTheme(Activity activity, @NonNull SiteModel site, @NonNul
         }
     }
 
-    private static void openWPCOMURL(Activity activity, String url, ThemeModel theme, SiteModel site) {
+    private static void openWPCOMURL(
+            Activity activity,
+            String url,
+            @NonNull ThemeModel theme,
+            SiteModel site
+    ) {
         if (activity == null) {
             AppLog.e(AppLog.T.UTILS, "ThemeWebActivity requires a non-null activity");
             return;
@@ -95,6 +104,7 @@ private static void openWPCOMURL(Activity activity, String url, ThemeModel theme
         activity.startActivityForResult(intent, ThemeBrowserActivity.ACTIVATE_THEME);
     }
 
+    @Nullable
     public static String getIdentifierForCustomizer(@NonNull SiteModel site, @NonNull ThemeModel theme) {
         if (site.isJetpackConnected()) {
             return theme.getThemeId();
@@ -103,8 +113,13 @@ public static String getIdentifierForCustomizer(@NonNull SiteModel site, @NonNul
         }
     }
 
-    public static String getUrl(@NonNull SiteModel site, @NonNull ThemeModel theme, @NonNull ThemeWebActivityType type,
-                                boolean isPremium) {
+    @Nullable
+    public static String getUrl(
+            @NonNull SiteModel site,
+            @NonNull ThemeModel theme,
+            @NonNull ThemeWebActivityType type,
+            boolean isPremium
+    ) {
         if (theme.isWpComTheme()) {
             switch (type) {
                 case PREVIEW:
@@ -113,10 +128,14 @@ public static String getUrl(@NonNull SiteModel site, @NonNull ThemeModel theme,
                             .format(THEME_URL_PREVIEW, UrlUtils.getHost(site.getUrl()), domain, theme.getThemeId());
                 case DEMO:
                     String url = theme.getDemoUrl();
-                    if (url.contains("?")) {
-                        return url + "&" + THEME_URL_DEMO_PARAMETER;
+                    if (url != null) {
+                        if (url.contains("?")) {
+                            return url + "&" + THEME_URL_DEMO_PARAMETER;
+                        } else {
+                            return url + "?" + THEME_URL_DEMO_PARAMETER;
+                        }
                     } else {
-                        return url + "?" + THEME_URL_DEMO_PARAMETER;
+                        return null;
                     }
                 case DETAILS:
                     return String.format(THEME_URL_DETAILS, theme.getThemeId());
@@ -126,7 +145,12 @@ public static String getUrl(@NonNull SiteModel site, @NonNull ThemeModel theme,
         } else {
             switch (type) {
                 case PREVIEW:
-                    return site.getAdminUrl() + "customize.php?theme=" + getIdentifierForCustomizer(site, theme);
+                    String identifier = getIdentifierForCustomizer(site, theme);
+                    if (identifier != null) {
+                        return site.getAdminUrl() + "customize.php?theme=" + identifier;
+                    } else {
+                        return null;
+                    }
                 case DEMO:
                     return site.getAdminUrl() + "themes.php?theme=" + theme.getThemeId();
                 case DETAILS:
diff --git a/build.gradle b/build.gradle
index c5b57f979717..44d6b2f96300 100644
--- a/build.gradle
+++ b/build.gradle
@@ -22,7 +22,7 @@ ext {
     automatticTracksVersion = '3.3.0'
     gutenbergMobileVersion = 'v1.109.1'
     wordPressAztecVersion = 'v1.8.0'
-    wordPressFluxCVersion = 'trunk-cdc8effb2affbb1c6bcf01f6606c847f87071d28'
+    wordPressFluxCVersion = 'trunk-b4e51008f7200eba1dfdd22ca370fce450ce93b0'
     wordPressLoginVersion = '1.10.0'
     wordPressPersistentEditTextVersion = '1.0.2'
     wordPressUtilsVersion = '3.10.0'