[FS#1118] bad argument #1 to 'tonumber' (string expected, got nil)

[LEDE Bugs]

The following task has a new comment added:

FS#1118 - bad argument #1 to 'tonumber' (string expected, got nil)
User who did this - Yousong Zhou (yousong)

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The change was just backported to lede-17.01 branch of luci repo.  Thanks for the contribution.
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=1118#comment4185