toRadixString method Null safety

Converts this to a string representation in the given radix.

In the string representation, lower-case letters are used for digits above '9', with 'a' being 10 an 'z' being 35.

The radix argument must be an integer in the range 2 to 36.

Example:

// Binary (base 2).
print(BigInt.from(12).toRadixString(2)); // 1100
print(BigInt.from(31).toRadixString(2)); // 11111
print(BigInt.from(2021).toRadixString(2)); // 11111100101
print(BigInt.from(-12).toRadixString(2)); // -1100
// Octal (base 8).
print(BigInt.from(12).toRadixString(8)); // 14
print(BigInt.from(31).toRadixString(8)); // 37
print(BigInt.from(2021).toRadixString(8)); // 3745
// Hexadecimal (base 16).
print(BigInt.from(12).toRadixString(16)); // c
print(BigInt.from(31).toRadixString(16)); // 1f
print(BigInt.from(2021).toRadixString(16)); // 7e5
// Base 36.
print(BigInt.from(35 * 36 + 1).toRadixString(36)); // z1