[Java] DictionaryEncoder doesn't crash when decoding index outside of Dictionary

Start at DictionaryEncoder.decode and reproduce the behavior with the provided testReferencingIndexOutOfBounds test. Confirm that an encoded index equal to the dictionary value count raises IllegalArgumentException with the expected message, while valid indices still decode normally.

Describe the bug, including details regarding any error messages, version, and platform.

Background

When manually creating an encoded vector, with values referencing indices in a Dictionary, it is possible to have values equal to valueCount of the Dictionary vector i.e. one index out of bounds. This is interpreted as a null value in the Dictionary.

Example

Dictionary

Encoded Vector - 1

Encoded Vector - 2

Encoded Vector - 3

Test to reproduce the error

    @Test
    public void testReferencingIndexOutOfBounds() {
        // Index at which the original value will be stored at in the dictionary
        var encodedIndex = 0;
        // The encoded value that references an index in the dictionary
        var indexReferenced = 1;

        try (final IntVector encodedVector = new IntVector("encodings", allocator);
             final VarCharVector dictionaryVector = newVarCharVector("dict", allocator); ) {
            var originalValue = "Foo";
            dictionaryVector.allocateNew(1);
            dictionaryVector.setValueCount(1);
            dictionaryVector.set(encodedIndex, originalValue.getBytes(StandardCharsets.UTF_8));

            encodedVector.allocateNew(1);
            encodedVector.setValueCount(1);
            encodedVector.set(0, indexReferenced);

            Dictionary dictionary =
                    new Dictionary(dictionaryVector, new DictionaryEncoding(1L, false, null));

            try (ValueVector decoded = DictionaryEncoder.decode(encodedVector, dictionary)) {
                fail("There should be an exception when decoding index outside dictionary's range.");
            } catch (Exception e) {
                assertEquals("Provided dictionary does not contain value for index " + indexReferenced, e.getMessage());
            }
        }
    }