minLength property Null safety
A string instance is valid against this keyword if its length is greater than, or equal to, the value of this keyword.
The length of a string instance is defined as the number of its
characters as defined by RFC 7159
The value of this keyword MUST be an integer. This integer MUST be greater than, or equal to, 0.
"minLength", if absent, may be considered as being present with integer value 0.