cannot save notebook: args-out-of-range

[sam-s]

When I try to save a notebook, I get this error:

Debugger entered--Lisp error: (args-out-of-range #<buffer *ein: http://remote-host:8080/foo.ipynb...
  #f(compiled-function (cell) "Grab text in the input area of the cell at point." #<bytecode 0x60703bd0e614828>)...
  apply(#f(compiled-function (cell) "Grab text in the input area of the cell at point." #<bytecode 0x60703bd0e61482
  ein:cell-get-text(#<ein:codecell ein:codecell-1ff2e91fa94c>)                                                     
  #f(compiled-function (cell wsidx) #<bytecode -0x60ead28ce7e11b>)(#<ein:codecell ein:codecell-1ff2e91fa94c> 0)    
  apply(#f(compiled-function (cell wsidx) #<bytecode -0x60ead28ce7e11b>) #<ein:codecell ein:codecell-1ff2e91fa94c> 
  ein:cell-to-nb4-json(#<ein:codecell ein:codecell-1ff2e91fa94c> 0)                                                
  #f(compiled-function (c) #<bytecode -0x14195cc094a6e0ce>)(#<ein:codecell ein:codecell-1ff2e91fa94c>)             
  mapcar(#f(compiled-function (c) #<bytecode -0x14195cc094a6e0ce>) (#<ein:codecell ein:codecell-1ff2e80fa9be> #<ein
  #f(compiled-function (ws wsidx) #<bytecode 0x1bae344327c77a2e>)(#<ein:worksheet ein:worksheet-1ff2e96fb6ec> 0)   
  apply(#f(compiled-function (ws wsidx) #<bytecode 0x1bae344327c77a2e>) #<ein:worksheet ein:worksheet-1ff2e96fb6ec>
  ein:worksheet-to-nb4-json(#<ein:worksheet ein:worksheet-1ff2e96fb6ec> 0)                                         
  ein:write-nbformat4-worksheets(#s(ein:$notebook :url-or-port "http://remote-host:8080" :notebook-
  ein:notebook-to-json(#s(ein:$notebook :url-or-port "http://remote-host:8080" :notebook-id nil :no
  ein:content-from-notebook(#s(ein:$notebook :url-or-port "http://remote-host:8080" :notebook-id ni
  ein:notebook-save-notebook(#s(ein:$notebook :url-or-port "http://remote-host:8080" :notebook-id n
  ein:notebook-save-notebook-command()                                                                             
  funcall-interactively(ein:notebook-save-notebook-command)                                                        
  call-interactively(ein:notebook-save-notebook-command)                                                           
  ein:notebook-save-notebook-command-km()                                                                          
  funcall-interactively(ein:notebook-save-notebook-command-km)                                                     
  call-interactively(ein:notebook-save-notebook-command-km nil nil)                                                
  command-execute(ein:notebook-save-notebook-command-km)

otherwise the notebook seems to work ok.