check command crashes on bad input

[gradha]

Some input crashes the nimrod check command:

$ babel install argument_parser
$ git clone https://github.com/gradha/kpop_blog.git
$ cd kpop_blog/
$ git checkout nimrod_check_crash 
$ nimrod check kpop_blog.nim 
kpop_blog.nim(144, 17) Error: undeclared identifier: 'commands'
kpop_blog.nim(144, 16) Error: type mismatch: got (PXmlNode, string, string)
but expected one of: 
kpop_blog.test_command(command: string, url: string, short_name: string): stmt

Traceback (most recent call last)
nimrod.nim(81)           nimrod
nimrod.nim(55)           HandleCmdLine
main.nim(402)            MainCommand
main.nim(53)             CommandCheck
modules.nim(193)         CompileProject
modules.nim(151)         compileModule
passes.nim(192)          processModule
passes.nim(136)          processTopLevelStmt
sem.nim(337)             myProcess
sem.nim(306)             SemStmtAndGenerateGenerics
semstmts.nim(1265)       semStmt
semexprs.nim(825)        semExprNoType
semexprs.nim(2009)       semExpr
semstmts.nim(1101)       semProc
semstmts.nim(1048)       semProcAux
semexprs.nim(1200)       semProcBody
semexprs.nim(1991)       semExpr
semstmts.nim(1226)       semStmtList
semexprs.nim(2001)       semExpr
semstmts.nim(669)        semFor
semstmts.nim(631)        semForVars
semstmts.nim(1265)       semStmt
semexprs.nim(825)        semExprNoType
semexprs.nim(1991)       semExpr
semstmts.nim(1227)       semStmtList
SIGSEGV: Illegal storage access. (Attempt to read from nil?)

[Araq]

Please provide a small(er) test program for this.