Dont store air only information in decoded block. This can be found out pretty easy by analysing the other fields if needed.

common/block.go

@@ -44,11 +44,10 @@ type (
 
 	DecodedBlock struct {
 		Version     byte
+		Transparent bool
 		MapContent  []byte
 		AirId       int32
 		IgnoreId    int32
-		AirOnly     bool
-		Transparent bool
 		IndexMap    map[int32]int32
 	}
 )
@@ -140,7 +139,6 @@ func NewDecodedBlock(data []byte, colors *Colors) (db *DecodedBlock, err error)
 
 	airId, ignoreId := int32(-1), int32(-1)
 	indexMap := make(map[int32]int32)
-	var airOnly bool
 	var transparent bool
 	if version >= 22 {
 		offset++
@@ -169,21 +167,23 @@ func NewDecodedBlock(data []byte, colors *Colors) (db *DecodedBlock, err error)
 				}
 			}
 		}
-		airOnly = airId != -1 && len(indexMap) == 0
 	}
 
 	db = &DecodedBlock{
 		Version:     version,
+		Transparent: transparent,
 		MapContent:  mapContent,
 		AirId:       airId,
 		IgnoreId:    ignoreId,
-		AirOnly:     airOnly,
-		Transparent: transparent,
 		IndexMap:    indexMap}
 
 	return
 }
 
+func (db *DecodedBlock) AirOnly() bool {
+	return db.AirId != -1 && len(db.IndexMap) == 0
+}
+
 func (db *DecodedBlock) Content(x, y, z int) (content int32, found bool) {
 	pos := z<<8 + y<<4 + x
 

common/renderer.go

@@ -215,7 +215,7 @@ func (r *Renderer) RenderBlock(block *Block, colors *Colors) (err error) {
 		return
 	}
 
-	if db.AirOnly {
+	if db.AirOnly() {
 		r.RejectedBlocks++
 		return
 	}