fix: add missing nil check (#971)

Co-authored-by: Andrey Nering <[email protected]>

Author: pd93

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 - Small bug fix: closing "Taskfile.yml" once we're done reading it
   ([#963](https://github.com/go-task/task/issues/963), [#964](https://github.com/go-task/task/pull/964) by @HeCorr).
+- Fixes a bug in v2 that caused a panic when using a `Taskfile_{{OS}}.yml` file
+  ([#961](https://github.com/go-task/task/issues/961), [#971](https://github.com/go-task/task/pull/971) by @pd93).
 - Fixed a bug where watch intervals set in the Taskfile were not being respected ([#969](https://github.com/go-task/task/pull/969), [#970](https://github.com/go-task/task/pull/970) by @pd93)
 - Add `--json` flag (alias `-j`) with the intent to improve support for code
   editors and add room to other possible integrations. This is basic for now,

taskfile/merge.go

@@ -45,7 +45,7 @@ func Merge(t1, t2 *Taskfile, includedTaskfile *IncludedTaskfile, namespaces ...s
 
 		// Set the task to internal if EITHER the included task or the included
 		// taskfile are marked as internal
-		task.Internal = task.Internal || includedTaskfile.Internal
+		task.Internal = task.Internal || (includedTaskfile != nil && includedTaskfile.Internal)
 
 		// Add namespaces to dependencies, commands and aliases
 		for _, dep := range task.Deps {