fix(utilities.js): Format string to lowercase before converting to ca…

…mel case and assert the string is a string

lib/utilities.js

@@ -10,7 +10,13 @@
 var _hyphenPattern = /-(.)/g;
 
 function camelCase(string) {
-    return string.replace(_hyphenPattern, function(_, character) {
+    if (typeof string !== 'string') { // null is an object
+        throw new TypeError('First argument must be a string');
+    }
+    if(string.indexOf('-') < 0) {
+        return string;
+    }
+    return string.toLowerCase().replace(_hyphenPattern, function(_, character) {
         return character.toUpperCase();
     });
 }