[BUGS] Fix bugs in using Graph and fast-spmm

[THINK2TRY]

Description

Checklist

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• The PR title starts with [$CATEGORY] (such as [Model], [Doc], [Feature], [Bugfix])
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented
• To my best knowledge, examples are either not affected by this change,
  or have been fixed to be compatible with this change
• Related issue is referred in this PR