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------------------------------------------------------------------------

campany-capf throwing an error in org-mode, while entering header args

#### Error in `*Messages*` buffer

```
Company: backend company-capf error "Wrong type argument: char-or-string-p,
nil" with args (prefix)
```

#### Steps to reproduce

- emacs -Q
- `(add-to-list 'load-path "~/.emacs.d/elpa/company-20210811.214/")`
- `M-x load-library` `company`
- Open a org-mode buffer
- enable `company-mode`
- enter the example below, you will get the error when typing `:var`

```
#+Name: get-env
#+begin_src emacs-lisp
(print "hello")
#+end_src

#+begin_src emacs-lisp :var env=get-env()
(print env)
#+end_src
```

#### Expected behavior
This should not trigger an error.

#### The error backtrace

```
Debugger entered--Lisp error: (wrong-type-argument char-or-string-p nil)
  org-babel-balanced-split(nil 32)
  #f(compiled-function (pair) #<bytecode -0x58ac6fff72dc116>)((:var))
  org-babel-parse-multiple-vars(((:var)))
  org-babel-parse-header-arguments(":var" light)
  #f(compiled-function (h) #<bytecode -0x1422a9568baa5a8e>)(":var")
  org-babel-get-src-block-info(light)
  pcomplete/org-mode/block-option/src()
  pcomplete-completions()
  pcomplete-completions-at-point()
  completion--capf-wrapper(pcomplete-completions-at-point optimist)
  company--capf-data-real()
  company--capf-data()
  company-capf(prefix)
  apply(company-capf prefix)
  company-call-backend-raw(prefix)
  company--force-sync(company-call-backend-raw (prefix) company-capf)
  company-call-backend(prefix)
  company--continue()
  company--perform()
  company-post-command()

```

with `C-M-i` I get this error in messages buffer

```
Error in post-command-hook (completion-in-region--postch):
(wrong-type-argument char-or-string-p nil)
```

trace -

```
Debugger entered--Lisp error: (wrong-type-argument char-or-string-p nil)
  org-babel-balanced-split(nil 32)
  #f(compiled-function (pair) #<bytecode 0x1086521bcdc902ea>)((:var))
  org-babel-parse-multiple-vars(((:var)))
  org-babel-parse-header-arguments(":var" light)
  #f(compiled-function (h) #<bytecode -0x1422a956b59ad8ce>)(":var")
  org-babel-get-src-block-info(light)
  pcomplete/org-mode/block-option/src()
  pcomplete-completions()
  pcomplete-completions-at-point()
  completion--capf-wrapper(pcomplete-completions-at-point optimist)
  company--capf-data-real()
  company--capf-data()
  company-capf(prefix)
  apply(company-capf prefix)
  company-call-backend-raw(prefix)
  company--force-sync(company-call-backend-raw (prefix) company-capf)
  company-call-backend(prefix)
  company--begin-new()
  company--perform()
  company-auto-begin()
  company-idle-begin(#<buffer test.org> #<window 3 on test.org> 230 95)
  apply(company-idle-begin (#<buffer test.org> #<window 3 on test.org> 230
95))
  timer-event-handler([t 24857 34109 966818 nil company-idle-begin
(#<buffer test.org> #<window 3 on test.org> 230 95) nil 848000])

```

Emacs  : GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
3.24.20, cairo version 1.16.0)
 of 2021-07-22
Package: Org mode version 9.4.6 (9.4.6-12-gdcc3a8-elpaplus @
/home/mypc/.emacs.d/elpa/org-plus-contrib-20210809/)