public boolean isSymbolNull ( String name ) { CommandSymbol s = findSymbol ( name ) ; if ( s == null ) return true ; if ( s instanceof VarCommand ) { VarCommand var = ( VarCommand ) s ; Value v = var . getValue ( this ) ; if ( v == null || v . get ( ) == null || v instanceof NilValue ) return true ; } return false ; }
Returns true if the symbol is null or has not been defined .