offset property Null safety

The offset in source where the error was detected.

A zero-based offset into the source that marks the format error causing this exception to be created. If source is a string, this should be a string index in the range 0 <= offset <= source.length.

If input is a string, the toString method may represent this offset as a line and character position. The offset should be inside the string, or at the end of the string.

May be omitted. If present, source should also be present if possible.