change prompt_numper type

prompt number type was number or string ('*', ' ')
require it to be either number, or null

IPython/nbformat/v3/v3.withref.json

@@ -1,166 +1,166 b''
 {
     "description": "custom json structure with references to generate notebook schema",
     "notebook":{
       "type": "object",
       "description": "notebook v3.0 root schema",
       "$schema": "http://json-schema.org/draft-03/schema",
       "id": "#notebook",
       "required": true,
       "additionalProperties": false,
       "properties":{
         "metadata": {
           "type": "object",
           "id": "metadata",
           "required": true,
           "description": "the metadata atribute can contain any additionnal information",
           "additionalProperties": true,
           "properties":{
             "name": {
               "id": "name",
               "description": "the title of the notebook",
               "type": "string",
               "id": "name",
               "required": true
             }
           }
         },
         "nbformat_minor": {
           "description": "Notebook format, minor number. Incremented for slight variation of notebook format.",
           "type": "number",
           "id": "nbformat_minor",
           "required": true
         },
         "nbformat": {
           "description": "Notebook format, major number. Incremented between backward incompatible change is introduced.",
           "type": "number",
           "id": "nbformat",
           "required": true
         },
         "worksheets": {
           "description": "Array of worksheet, not used by the current implementation of ipython yet",
           "type": "array",
           "id": "worksheets",
           "required": true,
           "items": {"$ref": "/worksheet"}
         }
       }
     },
 
     "worksheet": {
       "additionalProperties": false,
       "properties":{
         "cells": {
           "type": "array",
           "$schema": "http://json-schema.org/draft-03/schema",
           "description": "array of cells of the current worksheet",
           "id": "#cells",
           "required": true,
           "items": {"$ref": "/any_cell"}
 
         },
         "metadata": {
           "type": "object",
           "description": "metadata of the current worksheet",
           "id": "metadata",
           "required": true
         }
       }
     },
 
     "text_cell": {
       "type": "object",
       "description": "scheme for text cel and childrenm (level only optionnal argument for HEader cell)",
       "$schema": "http://json-schema.org/draft-03/schema",
       "id": "#cell",
       "required": true,
       "additionalProperties": false,
       "properties":{
         "cell_type": {
           "type": "string",
           "id": "cell_type",
           "required": true
         },
         "level": {
           "type": "number",
           "id": "level",
           "required": false
         },
         "metadata": {
           "type": "object",
           "id": "metadata",
           "required": true
         },
         "source": {
           "description": "for code cell, the source code",
           "type": "array",
           "id": "source",
           "required": true,
           "items":
             {
               "type": "string",
               "description": "each item represent one line of the source code written, terminated by \n",
               "id": "0",
               "required": true
             }
         }
       }
 
     },
 
     "any_cell": {
         "description": "Meta cell type that match any cell type",
         "type": [{"$ref": "/text_cell"},{"$ref":"/code_cell"}],
         "$schema": "http://json-schema.org/draft-03/schema"
     },
 
     "code_cell":{
       "type": "object",
       "$schema": "http://json-schema.org/draft-03/schema",
       "description": "Cell used to execute code",
       "id": "#cell",
       "required": true,
       "additionalProperties": false,
       "properties":{
         "cell_type": {
           "type": "string",
           "id": "cell_type",
           "required": true
         },
         "metadata": {
           "type": "object",
           "id": "metadata",
           "required": true
         },
         "collapsed": {
           "type": "boolean",
           "required": true
         },
         "input": {
           "description": "user input for text cells",
           "type": "array",
           "id": "input",
           "required": true,
           "items":
             {
               "type": "string",
               "id": "input",
               "required": true
             }
         },
         "outputs": {
             "description": "output for code cell, to be definied",
             "required": true,
             "type": "array"
         },
         "prompt_number": {
-            "type": ["number","string"],
+            "type": ["number","null"],
             "minimum": 0
         },
         "language": {
             "type": "string",
             "required": true
         }
       }
 
     }
 }