@Override
    public Map<String, String> parameters() {
        return parameters == null ? null : Collections.unmodifiableMap(parameters);
    }
@Test
    public void testParameters() {
        Map<String, String> expectedParameters = new HashMap<>();
        expectedParameters.put("foo", "val");
        expectedParameters.put("bar", "baz");

        Schema schema = SchemaBuilder.string().parameter("foo", "val").parameter("bar", "baz").build();
        assertTypeAndDefault(schema, Schema.Type.STRING, false, null);
        assertMetadata(schema, null, null, null, expectedParameters);

        schema = SchemaBuilder.string().parameters(expectedParameters).build();
        assertTypeAndDefault(schema, Schema.Type.STRING, false, null);
        assertMetadata(schema, null, null, null, expectedParameters);
    }