Be defensive about user input

README.md

@@ -28,7 +28,7 @@ BharyangAsc
 BharyangDesc
 BharyangGroup
 ```
-The `Bharyang` command uses a configuration value to determine whether the sort should be ascending ("asc") or descending ("desc"). It is ascending by default. Configure it using:
+The `Bharyang` command uses a configuration value to determine default sort type. The value can be one of `asc`, `desc` or `group`. For example, to set it to `desc`:
 ```vim
 let g:bharyang_default_sort_type="desc"
 ```

plugin/bharyang-vim.vim

@@ -16,6 +16,13 @@ let s:group = "group"
 " =========================
 
 function! s:Bharyang(type) range
+  " Check if the type is valid, because the user exposed global sort type might change it to something else.
+  if a:type !=# s:asc && a:type !=# s:desc && a:type !=# s:group
+    echoe "Sort type ".a:type." is not compatible with Bharyang. Use one of `asc`, `desc` or `group`."
+
+    return
+  endif
+
   if executable('bharyang')
     let l:sortedlines = s:SortLines(a:type, getline(a:firstline, a:lastline))
     let l:totallines = a:lastline - a:firstline + 1