rebalance fails if the reduce function of a view is invalid

Rebalance exited with reason {{{{{nocatch,
{invalid_value,
<<"builtin _sum function requires map values to be numbers or lists of numbers">>}},
[

{couch_query_servers, '-builtin_sum_rows/1-fun-0-',2}

,

{lists,foldl,3}

,

{couch_query_servers,builtin_reduce,4}

,

{couch_query_servers,reduce,3}

,

{couch_set_view_group, '-init_group/3-fun-4-',4}

,

{couch_btree,'-write_node/3-lc$^0/1-0-',5}

,

{couch_btree,write_node,3}

,

{couch_btree,modify_node,8}

]},
{gen_server,call,
[<18514.27178.1>,

{set_state,[], [9,10,11,12,26,27,28,29,30,31,32,33,34,52, 53,54,55,56,69,70,71,72,73,74,75,76,146, 147,155,156,157,158,159,160,161,162,247, 248,249,250,251,252,253,254,255], []}

,
infinity]}},
{gen_server,call,
[<18514.27164.1>,

{add_replicas, 115565932813024562229384322940239423064667081723753796902670741760461640834560}

,
infinity]}},
{gen_server,call,
[

{'capi_set_view_manager-default', 'ns_1@10.39.87.138'}

,

{wait_until_added,154}

,
infinity]}}