Unsatisfiable when field is nullable and size 0.

[MikiGrit]

Describe the bug As in the described in the title, the example code below will throw exception while I believe it should not.

• [x] I have checked that this issue has not already been reported.
• [x] I have confirmed this bug exists on the latest version of pandera.
• [ ] (optional) I have confirmed this bug exists on the master branch of pandera.

Note: Please read this guide detailing how to provide the necessary information for us to reproduce your bug.

Code Sample, a copy-pastable example

import pandera as pa
import pandera.typing as pt

class MySchema(pa.SchemaModel):
    myval: pt.Series[int] = pa.Field(nullable=True)

    class Config:
        strict = True
        coerce = True

MySchema.example(size=1)  # this passes
MySchema.example(size=0)  # this will throw Unsatisfiable

Desktop (please complete the following information):

• OS: [WSL on Windows 10]

[cosmicBboy]

thanks for filing this bug @MikiGrit! looking into this

[cosmicBboy]

638 should address this issue

[MikiGrit]

Thanks, for solving it promptly. Great work! :)