Null value is totally legal!
511873
public void setValue(String key, String value) {
        KeyValue kv = getKV(key);
        if (kv != null) {
            kv.setValue(value);
        } else if (key != null) {
            map.add(new KeyValue(key,value));
        }
    }
1070525
@NullSafe
  public static boolean areAnyNull(Object... values) {

    for (Object value : nullSafeArray(values)) {
      if (value == null) {
        return true;
      }
    }

    return false;
  }
675017
@Override
	public void setValue(StringValue value) {
		checkNotNull(value);
		setValue(value.value, 0, value.len);
	}
778108
private Double zeroIsNull(Double value)
   {
      if (value != null && value.doubleValue() == 0)
      {
         value = null;
      }
      return value;
   }
845267
public static Long checkNull(Long value, Long elseValue) {
        return isNull(value) ? elseValue : value;
    }
934581
public static Integer assign(final Integer value, final Integer defaultValueIfNull) {
        return value != null ? value : defaultValueIfNull;
    }
15369
public void writeNullableUTF(String str)
    {
        if (str == null)
            write(NULL_VALUE);
        else
        {
            write(NOT_NULL_VALUE);
            writeUTF(str);
        }
    }
1181604
@NotNull
    public static OptionalInt ofNullable(@Nullable Integer value) {
        return value == null ? EMPTY : new OptionalInt(value);
    }
1110208
private void checkForNull(String name, Object value) {
        if(name == null) {
            throw new NullPointerException("name must not be null");
        }
        if(value == null) {
            throw new NullPointerException("value must not be null");
        }
    }
313460
public static void checkNull(Object value, String message, Object... args) {
    if (value != null) {
      throw new IllegalArgumentException(String.format(message, args));
    }
  }
230285
@SuppressWarnings("nullness")
  private static <T> T castNonNull(@javax.annotation.Nullable T arg) {
    return arg;
  }
65241
@SuppressWarnings("unchecked")
	private <T> T nullFor(DataType dataType)
	{
		switch(dataType)
		{
			case Long: return (T)Long.valueOf(-1);
			default: return null;
		}
	}
753723
function isNull(value, message, id) {
    if (message === void 0) { message = ''; }
    if (id === void 0) { id = ''; }
    if (this.enabled && value !== null) {
        throw ValueException.unexpectedValue(assertionTypes.IS_NULL, value, null, message, id);
    }
}
420686
private Integer getNullOnValue(Integer value, int nullValue)
   {
      return (NumberHelper.getInt(value) == nullValue ? null : value);
   }
88193
@Nullable
    public static String nullableString(@Nullable String str) {
        return str == null || str.isEmpty() ? null : str;
    }
1017552
@CanIgnoreReturnValue
  public static <T> T checkNotNull(T reference) {
    if (reference == null) {
      throw new NullPointerException();
    }
    return reference;
  }
613037
public static Short checkNull(Short value, Short elseValue) {
        return isNull(value) ? elseValue : value;
    }