you should try to make some debug statements.
eg.
var DS_16_Empty = DS_16.isResultSetEmpty();
APPLICATION.createWarningMessage("ResultSetVisisble: DS_16" + DS_16_Empty);
var DS_30_Empty = DS_30.isResultSetEmpty();
APPLICATION.createWarningMessage("ResultSetVisisble: DS_30" + DS_30_Empty);
in your case if one of those is positive (true) the charts should be set to invisible.
what are your values?