Replaced NotImplemented with NotImplementedError

[Inzlinger]

Description

Replaced return NotImplemented with raise NotImplementedError

Issue/s resolved: #650

Type of change

• Bug fix (non-breaking change which fixes an issue)

Due Diligence

• All split configurations tested
• Multiple dtypes tested in relevant functions
• Documentation updated (if needed)
• Updated changelog.md under the title "Pending Additions"

Does this change modify the behaviour of other functions? If so, which?

no

[mtar]

Can one of the admins verify this patch?

[coquelin77]

crashing due to torch 1.6.0 updates, patch being implemented currently. there is nothing here which should change with the tests. Once the patch is up, then this will be merged

[codecov]

Codecov Report

Merging #651 into master will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #651   +/-   ##
=======================================
  Coverage   97.37%   97.37%           
=======================================
  Files          85       85           
  Lines       16646    16646           
=======================================
  Hits        16209    16209           
  Misses        437      437           

Impacted Files	Coverage Δ
heat/core/communication.py	89.88% <0.00%> (ø)

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