plotalot & line chart: because it replaces a path... - Joomla! Forum - community, help and support

i have problem line graphs driving me crazy . can not understand if problem related malfunction of google chart api or if have problems in sql code .
i have line graph 2 paths such , b ( example, red , b blue) , when both have non-zero values well, if null, path b drawn in place of it, red color, , label of a. big problem because makes ambiguous representation clients.
among many tests i've done in sql code i've tried using classical clause:
coalesce (count( field1 ) , '0 ' )
transforming the null value zero, nothing.
i try explain better... i've:

--plot 1--

select
month(data_avaria), count(num_avaria)
from avvisi
where
ciao='1'

--plot2 --

select
month(data_avaria), count(num_avaria)
from avvisi
where
ciao='2'

if plot1 not find value, not tracked, , in place inserted plot2, represented color , label of plot1, distorting display.

i not know how solve , , can not understand why behavior ... if track has no values , or these zero, should not traced , not replace first chart has values different 0 . not understand ... give me advice?

thanks lot