Invalid Pattern causes 500 Response

[Subzidion]

Reproduce:

Pattern: :digit:
Text: abc

Result: Server gives a 500 error with runtime error: invalid memory address or nil pointer dereference .

Environment:
Golang version 1.8
Linux 4.10.3-1-ARCH
Chromium 57.0.2987.110

[Subzidion]

Syntax Errors or compiler errors