🐭 热气球:

$var1=go from “V1” over E1 yield E1._dst as dst; $var2=go from $var1.dst over E2 yield E2._dst as dst; $var3=yield $var1.dst as dst union yield $var2.dst; go from $var3.dst over E3 reversely $var2 的 from id是引用$var1的结果，执行就报这个错：-1005:NULL', the srcs should be type of STRING, but wasNULL’