Prevent EncryptThis failures on blank tokens

[krotname]

Motivation

• The encryptThis helper could throw StringIndexOutOfBoundsException on whitespace-only input or when consecutive whitespace produced empty tokens, so make the function robust to such inputs.
• Tokenization should treat runs of whitespace as a single separator to preserve expected behavior for inputs with mixed or repeated whitespace.

Description

• Return early for blank inputs by changing the guard to if (text == null || text.isBlank()) return ""; in src/main/java/kyu6/EncryptThis.java.
• Change tokenization to split on runs of whitespace by using text.trim().split("\s+") to avoid empty tokens.
• Add regression tests in src/test/java/kyu6/EncryptThisTest.java that assert correct behavior for consecutive/mixed whitespace and that blank input returns an empty string.

Testing

• Ran the targeted test with mvn -q -Dtest=EncryptThisTest test, which passed.
• Ran the full suite with mvn -q test, which passed.
• Verified no diff check issues with git diff --check (no failures reported).

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Codex Task

[krotname]

Superseded by the validated combined merge in #115: #115