fix: handle `:var => nothing` provided to `remake` #643

Job	Run time
Tests (1, Core) / Tests - Core	15m 39s
Tests (1, Downstream) / Tests - Downstream	39m 42s
Tests (1, Python) / Tests - Python	17m 23s
Tests (1, QA) / Tests - QA	11m 55s
Tests (lts, Core) / Tests - Core	9m 29s
Tests (lts, Downstream) / Tests - Downstream	23m 57s
Tests (lts, Python) / Tests - Python	9m 12s
Tests (lts, QA) / Tests - QA	8m 24s
Tests (pre, Core) / Tests - Core	15m 50s
Tests (pre, Downstream) / Tests - Downstream	40m 54s
Tests (pre, Python) / Tests - Python	17m 50s
Tests (pre, QA) / Tests - QA	12m 47s
	3h 43m 2s

Provide feedback