if(NOT DEFINED ASN1C_OUTPUT_DIR)
    message(FATAL_ERROR "Missing ASN.1 output directory (ASN1C_OUTPUT_DIR)")
elseif(NOT DEFINED ASN1C_SOURCE_FILE)
    message(FATAL_ERROR "Missing ASN.1 source file (ASN1C_SOURCE_FILE)")
endif()

file(REMOVE_RECURSE ${ASN1C_OUTPUT_DIR})
file(WRITE ${ASN1C_SOURCE_FILE} "")