dvc status always mark a param as changed

[WestXu]

Bug Report

Please provide information about your setup

Output of dvc version:

$ dvc version
DVC version: 1.1.7
Python version: 3.8.3
Platform: Linux-4.19.104-microsoft-standard-x86_64-with-glibc2.10
Binary: False
Package: pip
Supported remotes: azure, gdrive, gs, hdfs, http, https, s3, ssh, oss
Cache: reflink - not supported, hardlink - supported, symlink - supported
Filesystem type (cache directory): ('9p', 'D:\\')
Repo: dvc, git
Filesystem type (workspace): ('9p', 'D:\\')

Additional Information (if any):

dvc status always gives me a "changed deps", when there isn't one. dvc commit / repro doesn't help.

$ dvc status
eval:                                                                           
        changed deps:
                params.yaml:
                        new:                eval.filter_limitup
$ dvc commit
dependencies ['params.yaml'] of stage: 'get_base_dv' changed. Are you sure you want to commit it? [y/n] y
dependencies ['params.yaml'] of stage: 'eval' changed. Are you sure you want to commit it? [y/n] y                                                                                 
$ dvc status
eval:                                                                           
        changed deps:
                params.yaml:
                        new:                eval.filter_limitup
$ dvc repro -P
Stage 'get_base_dv' didn't change, skipping                                     
Stage 'log_float_mv' didn't change, skipping
Stage 'lgt' didn't change, skipping
Stage 'margin_trade' didn't change, skipping
Stage 'alpha' didn't change, skipping
Stage 'industry' didn't change, skipping
Stage 'future_alpha' didn't change, skipping
Stage 'preprocess' didn't change, skipping
Stage 'train' didn't change, skipping
Restored stage 'eval' from run-cache
Skipping run, checking out outputs
$ dvc status
eval:                                                                           
        changed deps:
                params.yaml:
                        new:                eval.filter_limitup

Here is the content of my params.yaml:

start: 20200101
end: 20200630
universe: "000050.SH"
benchmark: "000905.SH"

eval:
  group: 5
  hold_days: 5
  filter_limitup: false

Here is the related content of my dvc.yaml:

stages:
  get_base_dv:
    cmd: ipython --pdb new_daily_model/get_base_dv.py
    deps:
    - new_daily_model/get_base_dv.py
    params:
    - benchmark
    - end
    - start
    - universe
    outs:
    - data/base_dv
  eval:
    cmd: ipython --pdb new_daily_model/eval.py
    deps:
    - data/prediction_sr.pkl
    - new_daily_model/eval.py
    params:
    - benchmark
    - eval.filter_limitup
    - eval.group
    - eval.hold_days
    - universe
    outs:
    - reports/fa.html
    metrics:
    - reports/metrics.json:
        cache: false

So there are at least 2 problems here:

1. dvc commit always shows the stage get_base_dv changed, even when dvc status didn't show that.
2. dvc status always shows the param eval.filter_limitup of stage eval changed, when actually wasn't.

[skshetry]

Issue is that we are skipping false values:

dvc/dvc/dependency/param.py

Lines 49 to 50 in 0899b27

	if value:
	self.info[param] = value

Should only have been:

self.info[param] = value