Preventing error when the branch isn't on upstream

themes/integral/fish_prompt.fish

@@ -6,18 +6,20 @@ end
 function _git_vs_upstream
   set count (command git rev-list --count --left-right "origin/$argv"...HEAD ^/dev/null)
 
-  switch $count
-    case "" # no upstream
-      echo ''
-    case "0?0" # equal to upstream
-      echo ''
-    case "0??" # ahead of upstream
-      echo 'u+'(echo $count | cut -f2)
-    case "??0" # behind upstream
-      echo 'u-'(echo $count | cut -f1)
-    case '???'      # diverged from upstream
-      echo 'u+'(echo $count | cut -f2)'-'(echo $count | cut -f1)
+  if count
+    switch $count
+      case "" # no upstream
+        echo ''
+      case "0?0" # equal to upstream
+        echo ''
+      case "0??" # ahead of upstream
+        echo 'u+'(echo $count | cut -f2)
+      case "??0" # behind upstream
+        echo 'u-'(echo $count | cut -f1)
+      case '???'      # diverged from upstream
+        echo 'u+'(echo $count | cut -f2)'-'(echo $count | cut -f1)
     end
+  end
 end
 
 function _is_git_dirty