fix error reporting when printing void

alib2cli/src/ast/command/PrintCommand.h

@@ -20,6 +20,9 @@ public:
 	CommandResult run ( Environment & environment ) const override {
 		std::shared_ptr < abstraction::Value > value = m_expr->translateAndEval ( environment );
+		if ( value->getType ( ) == std::string ( ext::to_string < void > ( ) ) )
+			throw std::invalid_argument ( "Printing void is not allowed." );
+
 		std::shared_ptr < abstraction::OperationAbstraction > res = abstraction::Registry::getValuePrinterAbstraction ( value->getType ( ) );
 		res->attachInput ( value, 0 );