DBMS_OUTPUT: NULL and empty string should be stored as NULL

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Description

Oracle treats empty strings as NULL. In DBMS_OUTPUT, both PUT_LINE('') and PUT_LINE(NULL) should store actual NULL values, which GET_LINE returns as SQL NULL.

Current Behavior

NULL values were being stored as empty strings internally.

Expected Behavior

• PUT_LINE('') should store NULL
• PUT_LINE(NULL) should store NULL
• GET_LINE should return SQL NULL for these values

Verification

Verified against Oracle 23.26 Free.

Fix

Commit 1c3339a in PR #15 addresses this issue.