src/main/java/org/apache/commons/text/StrBuilder.java [572:582]:
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        if (str == null) {
            return appendNull();
        }
        if (startIndex < 0 || startIndex > str.length()) {
            throw new StringIndexOutOfBoundsException("startIndex must be valid");
        }
        if (length < 0 || startIndex + length > str.length()) {
            throw new StringIndexOutOfBoundsException("length must be valid");
        }
        if (length > 0) {
            final int len = length();
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src/main/java/org/apache/commons/text/TextStringBuilder.java [674:684]:
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        if (str == null) {
            return appendNull();
        }
        if (startIndex < 0 || startIndex > str.length()) {
            throw new StringIndexOutOfBoundsException("startIndex must be valid");
        }
        if (length < 0 || startIndex + length > str.length()) {
            throw new StringIndexOutOfBoundsException("length must be valid");
        }
        if (length > 0) {
            final int len = length();
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