ttl-core/src/main/java/com/alibaba/ttl3/TransmittableThreadLocal.java [69:149]:
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    private final boolean disableIgnoreNullValueSemantics;

    /**
     * Default constructor. Create a {@link TransmittableThreadLocal} instance with "Ignore-Null-Value Semantics".
     * <p>
     * About "Ignore-Null-Value Semantics":
     *
     * <ol>
     *     <li>If value is {@code null}(check by {@link #get()} method), do NOT transmit this {@code ThreadLocal}.</li>
     *     <li>If set {@code null} value, also remove value(invoke {@link #remove()} method).</li>
     * </ol>
     * <p>
     * This is a pragmatic design decision:
     * <ol>
     * <li>use explicit value type rather than {@code null} value to express biz intent.</li>
     * <li>safer and more robust code(avoid {@code NPE} risk).</li>
     * </ol>
     * <p>
     * So it's strongly not recommended to use {@code null} value.
     * <p>
     * But the behavior of "Ignore-Null-Value Semantics" is NOT compatible with
     * {@link ThreadLocal} and {@link InheritableThreadLocal},
     * you can disable this behavior/semantics via using constructor {@link #TransmittableThreadLocal(boolean)}
     * and setting parameter {@code disableIgnoreNullValueSemantics} to {@code true}.
     * <p>
     * More discussion about "Ignore-Null-Value Semantics" see
     * <a href="https://github.com/alibaba/transmittable-thread-local/issues/157">Issue #157</a>.
     *
     * @see #TransmittableThreadLocal(boolean)
     */
    public TransmittableThreadLocal() {
        this(false);
    }

    /**
     * Constructor, create a {@link TransmittableThreadLocal} instance
     * with parameter {@code disableIgnoreNullValueSemantics} to control "Ignore-Null-Value Semantics".
     *
     * @param disableIgnoreNullValueSemantics disable "Ignore-Null-Value Semantics"
     * @see #TransmittableThreadLocal()
     */
    public TransmittableThreadLocal(boolean disableIgnoreNullValueSemantics) {
        this.disableIgnoreNullValueSemantics = disableIgnoreNullValueSemantics;
    }

    /**
     * Creates a transmittable thread local variable.
     * The initial value({@link #initialValue()}) of the variable is
     * determined by invoking the {@link #get()} method on the {@code Supplier}.
     *
     * @param <S>      the type of the thread local's value
     * @param supplier the supplier to be used to determine the initial value
     * @return a new transmittable thread local variable
     * @throws NullPointerException if the specified supplier is null
     * @see #withInitialAndGenerator(Supplier, UnaryOperator)
     */
    @NonNull
    @SuppressWarnings("ConstantConditions")
    public static <S> TransmittableThreadLocal<S> withInitial(@NonNull Supplier<? extends S> supplier) {
        if (supplier == null) throw new NullPointerException("supplier is null");

        return new SuppliedTransmittableThreadLocal<>(supplier, null, null);
    }

    /**
     * Creates a transmittable thread local variable.
     * The initial value({@link #initialValue()}) of the variable is
     * determined by invoking the {@link #get()} method on the {@code Supplier};
     * and the child value({@link #childValue(Object)}) and the transmittee value({@link #transmitteeValue(Object)}) of the variable is
     * determined by invoking the {@link UnaryOperator#apply(Object)} method on the {@code UnaryOperator}.
     *
     * @param <S>                                       the type of the thread local's value
     * @param supplier                                  the supplier to be used to determine the initial value
     * @param generatorForChildValueAndTransmitteeValue the value generator to be used to determine the child value and the transmittee value
     * @return a new transmittable thread local variable
     * @throws NullPointerException if the specified supplier or value generator is null
     * @see #withInitial(Supplier)
     */
    @NonNull
    @ParametersAreNonnullByDefault
    @SuppressWarnings("ConstantConditions")
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ttl2-compatible/src/main/java/com/alibaba/ttl/TransmittableThreadLocal.java [72:155]:
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    private final boolean disableIgnoreNullValueSemantics;

    /**
     * Default constructor. Create a {@link TransmittableThreadLocal} instance with "Ignore-Null-Value Semantics".
     * <p>
     * About "Ignore-Null-Value Semantics":
     *
     * <ol>
     *     <li>If value is {@code null}(check by {@link #get()} method), do NOT transmit this {@code ThreadLocal}.</li>
     *     <li>If set {@code null} value, also remove value(invoke {@link #remove()} method).</li>
     * </ol>
     * <p>
     * This is a pragmatic design decision:
     * <ol>
     * <li>use explicit value type rather than {@code null} value to express biz intent.</li>
     * <li>safer and more robust code(avoid {@code NPE} risk).</li>
     * </ol>
     * <p>
     * So it's strongly not recommended to use {@code null} value.
     * <p>
     * But the behavior of "Ignore-Null-Value Semantics" is NOT compatible with
     * {@link ThreadLocal} and {@link InheritableThreadLocal},
     * you can disable this behavior/semantics via using constructor {@link #TransmittableThreadLocal(boolean)}
     * and setting parameter {@code disableIgnoreNullValueSemantics} to {@code true}.
     * <p>
     * More discussion about "Ignore-Null-Value Semantics" see
     * <a href="https://github.com/alibaba/transmittable-thread-local/issues/157">Issue #157</a>.
     *
     * @see #TransmittableThreadLocal(boolean)
     */
    public TransmittableThreadLocal() {
        this(false);
    }

    /**
     * Constructor, create a {@link TransmittableThreadLocal} instance
     * with parameter {@code disableIgnoreNullValueSemantics} to control "Ignore-Null-Value Semantics".
     *
     * @param disableIgnoreNullValueSemantics disable "Ignore-Null-Value Semantics"
     * @see #TransmittableThreadLocal()
     * @since 2.11.3
     */
    public TransmittableThreadLocal(boolean disableIgnoreNullValueSemantics) {
        this.disableIgnoreNullValueSemantics = disableIgnoreNullValueSemantics;
    }

    /**
     * Creates a transmittable thread local variable.
     * The initial value({@link #initialValue()}) of the variable is
     * determined by invoking the {@link #get()} method on the {@code Supplier}.
     *
     * @param <S>      the type of the thread local's value
     * @param supplier the supplier to be used to determine the initial value
     * @return a new transmittable thread local variable
     * @throws NullPointerException if the specified supplier is null
     * @see #withInitialAndCopier(Supplier, TtlCopier)
     * @since 2.12.2
     */
    @NonNull
    @SuppressWarnings("ConstantConditions")
    public static <S> TransmittableThreadLocal<S> withInitial(@NonNull Supplier<? extends S> supplier) {
        if (supplier == null) throw new NullPointerException("supplier is null");

        return new SuppliedTransmittableThreadLocal<>(supplier, null, null);
    }

    /**
     * Creates a transmittable thread local variable.
     * The initial value({@link #initialValue()}) of the variable is
     * determined by invoking the {@link #get()} method on the {@code Supplier};
     * and the child value({@link #childValue(Object)}) and the transmitting value({@link #copy(Object)}) of the variable is
     * determined by invoking the {@link  TtlCopier#copy(Object)} method on the {@code TtlCopier}.
     *
     * @param <S>                        the type of the thread local's value
     * @param supplier                   the supplier to be used to determine the initial value
     * @param copierForChildValueAndCopy the ttl copier to be used to determine the child value and the transmitting value
     * @return a new transmittable thread local variable
     * @throws NullPointerException if the specified supplier or copier is null
     * @see #withInitial(Supplier)
     * @since 2.12.3
     */
    @NonNull
    @ParametersAreNonnullByDefault
    @SuppressWarnings("ConstantConditions")
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