:Plug throws error for invalid option

plug.vim

@@ -632,17 +632,34 @@ function! plug#(repo, ...)
     let g:plugs[name] = spec
     let s:loaded[name] = get(s:loaded, name, 0)
   catch
-    return s:err(v:exception)
+    return s:err(repo . ' ' . v:exception)
   endtry
 endfunction
 
 function! s:parse_options(arg)
   let opts = copy(s:base_spec)
   let type = type(a:arg)
+  let opt_errfmt = 'Invalid argument for "%s" option of :Plug (expected: %s)'
   if type == s:TYPE.string
+    if empty(a:arg)
+      throw printf(opt_errfmt, 'tag', 'string')
+    endif
     let opts.tag = a:arg
   elseif type == s:TYPE.dict
     call extend(opts, a:arg)
+    for opt in ['branch', 'tag', 'commit', 'rtp', 'dir', 'as']
+      if has_key(opts, opt)
+      \ && (type(opts[opt]) != s:TYPE.string || empty(opts[opt]))
+        throw printf(opt_errfmt, opt, 'string')
+      endif
+    endfor
+    for opt in ['on', 'for']
+      if has_key(opts, opt)
+      \ && type(opts[opt]) != s:TYPE.list
+      \ && (type(opts[opt]) != s:TYPE.string || empty(opts[opt]))
+        throw printf(opt_errfmt, opt, 'string or list')
+      endif
+    endfor
     if has_key(opts, 'dir')
       let opts.dir = s:dirpath(s:plug_expand(opts.dir))
     endif

test/workflow.vader

@@ -49,11 +49,19 @@ Execute (Test Plug command):
   AssertEqual 'no-t_co', g:plugs['seoul256.vim'].branch
 
 ^ Git repo with tag (DEPRECATED. USE TAG OPTION)
+  redir => out
+  Plug 'foo/bar.vim', ''
+  redir END
+  Assert out =~ 'Invalid argument for "tag" option of :Plug (expected: string)'
   Plug 'junegunn/goyo.vim', '1.5.2'
   AssertEqual 'file:///tmp/vim-plug-test/junegunn/goyo.vim', g:plugs['goyo.vim'].uri
   AssertEqual join([g:temp_plugged, 'goyo.vim/'], '/'), g:plugs['goyo.vim'].dir
   AssertEqual '1.5.2', g:plugs['goyo.vim'].tag
 
+  redir => out
+  Plug 'foo/bar.vim', {'tag': ''}
+  redir END
+  Assert out =~ 'Invalid argument for "tag" option of :Plug (expected: string)'
   Plug 'junegunn/goyo.vim', { 'tag': '1.5.3' } " Using tag option
   AssertEqual '1.5.3', g:plugs['goyo.vim'].tag
 
@@ -77,6 +85,18 @@ Execute (Test Plug command):
 
 Execute (Plug command with dictionary option):
   Log string(g:plugs)
+  for opt in ['branch', 'tag', 'commit', 'rtp', 'dir', 'as']
+    redir => out
+    Plug 'foo/bar.vim', {opt: ''}
+    redir END
+    Assert out =~ 'Invalid argument for "'.opt.'" option of :Plug (expected: string)'
+  endfor
+  for opt in ['on', 'for']
+    redir => out
+    Plug 'foo/bar.vim', {opt: ''}
+    redir END
+    Assert out =~ 'Invalid argument for "'.opt.'" option of :Plug (expected: string or list)'
+  endfor
   Plug 'junegunn/seoul256.vim', { 'branch': 'no-t_co', 'rtp': '././' }
   AssertEqual join([g:temp_plugged, 'seoul256.vim/'], '/'), g:plugs['seoul256.vim'].dir
   AssertEqual '././', g:plugs['seoul256.vim'].rtp