graph add --merge-entities does not properly merge entities

[YaroShkvorets]

Probably related to #1839 ?

We have 2 mainnet contracts:
0xdAC17F958D2ee523a2206206994597C13D831ec7 - USDT with 10 events
0x514910771AF9Ca656af840dff83E8264EcF986CA - LINK with 2 events that already exist in USDT but different parameters

Trying to graph init on one contract and then graph add --merge-entities another.
Expected: USDT + LINK and LINK + USDT to be functionally the same
Getting:

• LINK + USDT - works and merges entities with parameters successfully
• USDT + LINK - works but entities are not merged

i.e. this works as expected:

graph init link link --from-contract=0x514910771AF9Ca656af840dff83E8264EcF986CA --protocol=ethereum --start-block=111 --contract-name=USDT --index-events  --network=mainnet
graph add 0xdAC17F958D2ee523a2206206994597C13D831ec7 --merge-entities

This does not:

graph init usdt usdt --from-contract=0xdAC17F958D2ee523a2206206994597C13D831ec7 --protocol=ethereum --start-block=222 --contract-name=USDT --index-events  --network=mainnet
graph add 0x514910771AF9Ca656af840dff83E8264EcF986CA --merge-entities