make sepolia and mainnet hardhat networks optional

README.md

@@ -107,6 +107,12 @@ or
 
         npm install
 
+1. Copy the example configuration file
+
+        cp .env.example .env
+
+1. In `.env`, set a value for `SEED_PHRASE` or `LOCAL_PRIVATE_KEY`
+
 1. Run a hardhat node
 
         npx hardhat node

ethereum/hardhat.config.js

@@ -12,14 +12,18 @@ module.exports = {
         : [process.env.LOCAL_PRIVATE_KEY],
       chainId: 1337,
     },
-    sepolia: {
-      url: `https://sepolia.infura.io/v3/${process.env.INFURA_API_KEY}`,
-      accounts: [process.env.SEPOLIA_PRIVATE_KEY],
-    },
-    mainnet: {
-      url: `https://mainnet.infura.io/v3/${process.env.INFURA_API_KEY}`,
-      accounts: [process.env.MAINNET_PRIVATE_KEY],
-    },
+    ...process.env.SEPOLIA_PRIVATE_KEY ? {
+      sepolia: {
+        url: `https://sepolia.infura.io/v3/${process.env.INFURA_API_KEY}`,
+        accounts: [process.env.SEPOLIA_PRIVATE_KEY],
+      },
+    } : {},
+    ...process.env.MAINNET_PRIVATE_KEY ? {
+      mainnet: {
+        url: `https://mainnet.infura.io/v3/${process.env.INFURA_API_KEY}`,
+        accounts: [process.env.MAINNET_PRIVATE_KEY],
+      },
+    } : {},
   },
   etherscan: {
     apiKey: {