public StrBuilder append(String str) { if (str == null) {
public StrBuilder append(Object obj) { if (obj == null) {
    public StrBuilder append(String str) {        if (str == null) {            return appendNull();        }        int strLen = str.length();        if (strLen > 0) {            int len = length();            ensureCapacity(len + strLen);            str.getChars(0, strLen, buffer, len);            size += strLen;        }        return this;    }