diff --git a/lib/index.js b/lib/index.js
index a0e795f..072f611 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -173,6 +173,10 @@ var convert = function(type, value, from, to, max_calls){
 
 
 var get_variations = function(unit){
+    if(unit == null || unit == undefined){
+	return [];
+    }
+
     var variations = [unit];
     if(unit.length == 2){
 	return variations;
@@ -231,12 +235,12 @@ return module.exports = {
 	return unit_database;
     },
     getUnitType: function(unit){
-	var type = determine_type(get_variations(unit));
-	if(!type){
+	var types = determine_type(get_variations(unit));
+	if(!types){
 	    return null;
 	}
 
-	return type;
+	return types;
     },
     convert: function(str){
 	var value, from, to;