The second parameter of RiakMapReduce::add when not null should be forced a sting when the key is an integer. 
The second parameter of RiakMapReduce::add when not null should be forced a sting when the key is an integer. 

Prior to this change, one would get the following error message:

An error occurred parsing the "inputs" field.
Unrecognized format of input element:
   ["mybucket",123,null]

Valid formats are:
   [Bucket, Key]
   [Bucket, Key, KeyData]
where Bucket and Key are strings

0x20h/riak-php-client,basho/riak-php-client