handle OR'd tags where the first tag matches nothing : assignment to nil map panic

tag/process.go

@@ -40,19 +40,36 @@ func processQueries(tagmap map[string]Set, query Query) Set {
 
 	// initialize as first query
 	q := query.Tags[0]
+	// NOTE: clone so that we don't accidentally overwrite the incoming tagmap
+	set = maps.Clone(tagmap[q])
 
 	// empty query
 	// TODO: do I want to handle WILD and a tag? Actual regex?
-	if query.Op == WILD && q == "" {
+	if len(query.Tags) == 1 && query.Op == WILD && q == "" {
 		// NOTE: this is all files with at least one tag and therefore of value:
 		set.Union(slices.Collect(maps.Values(tagmap))...)
 		return set
 	}
+	// no need for set logic in this case:
+	if len(query.Tags) == 1 {
+		return set
+	}
+	// if first query matches nothing: set will be nil and Union will fail:
+	// TODO: solve this in set.Union by moving to pointer receiver.
+	if set == nil {
+		for _, t := range query.Tags {
+			if tagmap[t] != nil {
+				set = tagmap[t]
+				break
+			}
+		}
+	}
+	// all tagmap[q] are still nil:
+	if set == nil {
+		return set
+	}
 
-	// NOTE: clone so that we don't accidentally overwrite the incoming tagmap
-	set = maps.Clone(tagmap[q])
-	// when queries < 2, this won't run
-	for i := 1; i < len(query.Tags); i++ {
+	for i := 0; i < len(query.Tags); i++ {
 		q = query.Tags[i]
 		switch query.Op {
 		case OR: