common: Add 'zero'/'empty' static methods

These methods are being added for:

- Being helpful/useful to subgraph developers
- Ease some zero/empty value initialization in graph-cli

common/collections.ts

@@ -18,6 +18,10 @@ export class ByteArray extends Uint8Array {
     return self
   }
 
+  static empty(): ByteArray {
+    return ByteArray.fromI32(0)
+  }
+
   /**
    * Input length must be even.
    */
@@ -146,6 +150,10 @@ export class Bytes extends ByteArray {
   static fromUint8Array(uint8Array: Uint8Array): Bytes {
     return changetype<Bytes>(uint8Array)
   }
+
+  static empty(): Bytes {
+    return changetype<Bytes>(ByteArray.empty())
+  }
 }
 
 /**

common/numbers.ts

@@ -34,6 +34,16 @@ export class Address extends Bytes {
   static fromString(s: string): Address {
     return changetype<Address>(typeConversion.stringToH160(s))
   }
+
+  static zero(): Address {
+    let self = new ByteArray(20)
+
+    for (let i = 0; i < 20; i++) {
+      self[i] = 0
+    }
+
+    return changetype<Address>(self)
+  }
 }
 
 /** An arbitrary size integer represented as an array of bytes. */
@@ -43,6 +53,10 @@ export class BigInt extends Uint8Array {
     return BigInt.fromByteArray(byteArray)
   }
 
+  static zero(): BigInt {
+    return BigInt.fromI32(0)
+  }
+
   /**
    * `bytes` assumed to be little-endian. If your input is big-endian, call `.reverse()` first.
    */
@@ -280,6 +294,10 @@ export class BigDecimal {
     return bigDecimal.fromString(s)
   }
 
+  static zero(): BigDecimal {
+    return new BigDecimal(BigInt.zero())
+  }
+
   toString(): string {
     return bigDecimal.toString(this)
   }