Support empty input data.

src/index.coffee

@@ -112,6 +112,11 @@ class XlsxWriter
         if @cellLabelMap[col]
             colIndex = @cellLabelMap[col]
         else
+            if col == 0
+                # Provide a fallback for empty spreadsheets
+                row = 1
+                col = 1
+
             input = (+col - 1).toString(26)
             while input.length
                 a = input.charCodeAt(input.length - 1)

test/common.coffee

@@ -25,12 +25,14 @@ module.exports = (name, data) ->
 
         it 'Should have header row', ->
             assert(result.length >= 1, "Should have header row")
+            return if !data[0]
 
             for key, index in _.keys(data[0])
                 assert.equal(result[0][index], key)
 
         it 'Should contain right values', ->
             assert.equal(result.length, data.length + 1)
+            return if !data[0]
 
             for row, rowNr in result
                 continue if rowNr == 0 # Header

test/dimensions_test.coffee

@@ -5,6 +5,9 @@ assert = require('assert')
 describe 'Dimensions', ->
     writer = new XlsxWriter('tmp.xslx')
 
+    it 'Calculates 0x0 dimensions', ->
+        assert.equal(writer.dimensions(0, 0), 'A1:A1')
+
     it 'Calculates 1x1 dimensions', ->
         assert.equal(writer.dimensions(1, 1), 'A1:A1')
 

test/empty_test.coffee

@@ -0,0 +1,4 @@
+test = require('./common')
+
+test 'empty-test', [
+]