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kotlinlang

hi! not sure if this should be in <#C7L3JB43G|>, but I'm trying to invoke the kotlin compiler "manually" to integrate it with a build system, and it's causing some weird output: ```error: unresolved reference: !
  if (!isValid(address))

error: type mismatch: inferred type is kotlin.String but java.lang.String was expected
  return "Not a valid address"```
is there some flag I'm missing / is there a "user's guide" for integrating kotlin with a build tool?