support empty transactionId

[koxudaxi]

Related Issue

#41

[codecov]

Codecov Report

Merging #76 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #76   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           13        13           
  Lines          691       702   +11     
  Branches        87        89    +2     
=========================================
+ Hits           691       702   +11     

Impacted Files	Coverage Δ
local_data_api/models.py	100.00% <100.00%> (ø)

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