accommodate NULL at the compiler level for literal_render

accommodate NULL at the compiler level for literal_render

Added compiler-level None/NULL handling for the "literal processors" of all
datatypes that include literal processing, that is, where a value is
rendered inline within a SQL statement rather than as a bound parameter,
for all those types that do not feature explicit "null value" handling.
Previously this behavior was undefined and inconsistent.

Fixes: #10535
Change-Id: I746d19d6cec2aefa3244f5e5a6970950a698d96c