public Symbol normalizeSymbol(Function symbol) {
assert (symbol != null);
assert (symbol.arguments().size() == 1);
Symbol arg = symbol.arguments().get(0);
if (arg.equals(Literal.NULL) || arg.symbolType() == SymbolType.DYNAMIC_REFERENCE) {
return Literal.newLiteral(true);
} else if (arg.symbolType().isValueSymbol()) {
return Literal.newLiteral(((Input) arg).value() == null);
}
return symbol;