Empty (predicate) override option doesn't clear previous values

[xparq]

These all fail (note: the test app has --greedy and -G as "greedy", but that doesn't matter here):

SH echo Override with empty, long greedy
RUN args-test --greedy 1 2 3 --greedy
EXPECT "Override with empty, long
-------- NAMED (1):
greedy
-------- POSITIONAL (0):
"

Should also verify this then:

SH echo Override with empty, short greedy
RUN args-test --G 1 2 3 -G
EXPECT "Override with empty, long
-------- NAMED (1):
G
-------- POSITIONAL (0):
"

And of course the simplest case of empty override:

RUN args-test --thing=1 --thing
EXPECT "Override with empty, long
-------- NAMED (1):
thing
-------- POSITIONAL (0):
"

---

Non-greedy known ones can't be empty (--take-two takes 2)?

SH echo Override with empty, long (ERROR: insufficient parameters)
RUN args-test --take-two 1 2 3 --take-two
EXPECT "Override with empty, long
-------- NAMED (1):
take-two
-------- POSITIONAL (0):
"

...and:

SH echo Override with empty, short
RUN args-test --G 1 2 3 -G
EXPECT "Override with empty, long
-------- NAMED (1):
G
-------- POSITIONAL (0):
"