Why adding (char*)0 to JsonArray returns false?

Created by: dyarkovoy

According to the docs, JsonVariant::add() returns

• true if the value was successfully added.
• false if there was not enough memory in the JsonDocument.

However, when I do array.add((char*)0), the returned value is always false, even if the new slot was added successfully. I traced it down to this piece in VariantData.hpp:

  template <typename TStoragePolicy>
  bool setString(const char *s, TStoragePolicy storage_policy) {
    if (s) {
      setString(make_not_null(s), storage_policy);
      return true;
    } else {
      setType(VALUE_IS_NULL);
      return false;
    }
  }

I guess this assumes that if s==nullptr, then we could not allocate mem somewhere earlier, But what if we purposefully pass nullptr? This may seem like a minor glitch, but my use case is to make sure there's always enough space in the doc when populating it, so I check the return of every set() and add() and throw if any returns false, to preserve document consistency.

Maybe there's anoter [proper] way to assign null to a JsonVariant?

If I'm not overlooking something and this is a glitch indeed, then it raises another question, maybe we should have a special-case-null-variant static, or separate setNull() / addNull() methods, like the isNull() we have already?