I try to port LZString 1.4.4 to Qt, but I struggle with _decompress() function.
There is a loop at the beginning (line 346):

var dictionary = []

for (i = 0; i < 3; i += 1) {
  dictionary[i] = i;
}

which inserts some integers: 0, 1, 2 to dictionary array.
Later there are some strings added to this dictionary too (line 438, 456):

dictionary[dictSize++] = f(bits);

Finally at the end of _decompress() there is condition (line 469):

if (dictionary[c]) {
  entry = dictionary[c];
} else {
  ...
}

What is the purpose for this codition ?
Currently it returns false for dictionary[c] == null, c >= dictionary.length and for c=0 (because dictionary[0] contains 0).

Shouldn't the for loop at the beginning of _decompress() be like:

for (i = 0; i < 3; i += 1) {
  dictionary[i] = f(i);    // or maybe: dictionary[i] = ''+i ???
}

so it would only contains strings ?

Different ports have different implementations:

diogoduailibe/lzstring4j:

List<String> dictionary = new ArrayList<String>(200);
for (int i = 0; i < 3; i += 1) {
   dictionary.add(i, "");
}

(...)

if (d < dictionary.size() && dictionary.get(d) != null) {
   entry = dictionary.get(d);
} else {
   (...)
}

rufushuang/lz-string4java:

ArrayList<String> result = new ArrayList<String>();
for (int i = 0; i < 3; i += 1) {
   dictionary.add(i, f(i));
}

(...)

if (cc < dictionary.size() && dictionary.get(cc) != null) {
   entry = dictionary.get(cc);
} else {
   (...)
}

jawa-the-hutt/lz-string-csharp:

List<string> dictionary = new List<string>();
for (i = 0; i < 3; i++)
{
   dictionary.Add(i.ToString());
}

(...)

if (dictionary.Count - 1 >= c) // if (dictionary[c] ) <------- original Javascript Equivalant
{
   entry = dictionary[c];
}
else
   (...)
}

kreudom/lz-string-csharp:

Dictionary<int, string> dictionary = new Dictionary<int, string>();
for (i = 0; i < 3; i++)
{
   dictionary[i] = Convert.ToChar(i).ToString();
}

(...)

if(dictionary.ContainsKey(c))
{
   entry = dictionary[c];
}
else
{
   (...)
}