public static final long MIN_VALUE_UINT32 = 0;
public static final long MAX_VALUE_UINT32 = 4294967293L; // 0xFFFFFFFD
public static final long NULL_VALUE_UINT32 = 4294967294L; // 0xFFFFFFFE

There is some code that define some constant value of basic type of number in PrimitiveValue.java.I can't understand why NULL_VALUE_UINT32 is 0xFFFFFFFE(2 ^ 32 - 2) instead of 0xFFFFFFFF(2 ^ 32 - 1), but NULL_VALUE_UINT16 is 65535(2 ^ 16 - 1) and NULL_VALUE_UINT8 is 255(2 ^ 8 - 1).

The documentation is in Range attributes for integer fields