Removed unneeded code

Author: ankane

src/mikro-orm/halfvec.js

@@ -10,9 +10,6 @@ export class HalfvecType extends Type {
   }
 
   convertToJSValue(value, platform) {
-    if (value === null) {
-      return null;
-    }
     return halfvecFromSql(value);
   }
 

src/mikro-orm/sparsevec.js

@@ -11,9 +11,6 @@ export class SparsevecType extends Type {
 
   // @ts-ignore
   convertToJSValue(value, platform) {
-    if (value === null) {
-      return null;
-    }
     return sparsevecFromSql(value);
   }
 

src/mikro-orm/vector.js

@@ -10,9 +10,6 @@ export class VectorType extends Type {
   }
 
   convertToJSValue(value, platform) {
-    if (value === null) {
-      return null;
-    }
     return vectorFromSql(value);
   }