diff -ru a/webapp/content/js/composer_widgets.js b/webapp/content/js/composer_widgets.js
--- a/webapp/content/js/composer_widgets.js 2010-02-26 16:12:54.000000000 +0000
+++ b/webapp/content/js/composer_widgets.js 2010-09-15 07:03:56.000000000 +0000
@@ -531,6 +531,7 @@
                   {text: 'Line Width', handler: this.applyFuncToEachWithInput('lineWidth', 'Please enter a line width for this graph target')},
                   {text: 'Dashed Line', handler: this.applyFuncToEach('dashed')},
                   {text: 'Keep Last Value', handler: this.applyFuncToEach('keepLastValue')},
+                  {text: 'Fill Value', handler: this.applyFuncToEachWithInput('fillValue', 'Please enter a value to fill. Leave blank for 0', true)},
                   {text: 'Substring', handler: this.applyFuncToEachWithInput('substr', 'Enter a starting position')}
                 ]
               }
diff -ru a/webapp/graphite/render/functions.py b/webapp/graphite/render/functions.py--- a/webapp/graphite/render/functions.py   2010-01-25 05:21:31.000000000 +0000
+++ b/webapp/graphite/render/functions.py   2010-09-15 06:58:27.000000000 +0000
@@ -141,6 +141,15 @@
       series[i] = value
   return seriesList

+def fillValue(seriesList, placeholder=0):
+  for series in seriesList:
+    series.name = "fillValue(%s, %i)" % (series.name, placeholder)
+    for i,value in enumerate(series):
+      if value is None and i != 0:
+        value = placeholder
+      series[i] = value
+  return seriesList
+
 def asPercent(seriesList1,seriesList2orNumber):
   assert len(seriesList1) == 1, "asPercent series arguments must reference *exactly* 1 series"
   series1 = seriesList1[0]
@@ -490,6 +499,7 @@
   'alias' : alias,
   'cumulative' : cumulative,
   'keepLastValue' : keepLastValue,
+  'fillValue' : fillValue,
   'drawAsInfinite' : drawAsInfinite,
   'lineWidth' : lineWidth,
   'dashed' : dashed,