Omit MultiLineBuilder variable if empty (#103) #456

Job	Run time
windows-unittest-matrix (receiver-0)	17m 40s
windows-unittest-matrix (receiver-1)	18m 5s
windows-unittest-matrix (processor)	17m 48s
windows-unittest-matrix (exporter)	17m 58s
windows-unittest-matrix (extension)	17m 6s
windows-unittest-matrix (internal)	17m 51s
windows-unittest-matrix (pkg)	17m 46s
windows-unittest-matrix (cmd)	18m 3s
windows-unittest-matrix (other)	18m 1s
windows-unittest	0s
	2h 40m 18s

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