diff --git a/scripts/common/easing.lua b/scripts/common/easing.lua
index 11717b2..f02b327 100644
--- a/scripts/common/easing.lua
+++ b/scripts/common/easing.lua
@@ -41,16 +41,25 @@ local function linear(t, b, c, d)
 end
 
 local function inQuad(t, b, c, d)
+  b = b or 0
+  c = c or 1
+  d = d or 1
   t = t / d
   return c * (t ^ 2) + b
 end
 
 local function outQuad(t, b, c, d)
+  b = b or 0
+  c = c or 1
+  d = d or 1
   t = t / d
   return -c * t * (t - 2) + b
 end
 
 local function inOutQuad(t, b, c, d)
+  b = b or 0
+  c = c or 1
+  d = d or 1
   t = t / d * 2
   if t < 1 then
     return c / 2 * (t ^ 2) + b
@@ -60,6 +69,9 @@ local function inOutQuad(t, b, c, d)
 end
 
 local function outInQuad(t, b, c, d)
+  b = b or 0
+  c = c or 1
+  d = d or 1
   if t < d / 2 then
     return outQuad (t * 2, b, c / 2, d)
   else