Fix toBn bug

Fix $bn not define when call toBn with BigNumber instance.

src/Utils.php

@@ -235,11 +235,8 @@ class Utils
      */
     public static function toString($value)
     {
-        try {
-            $value = (string) $value;
-        } catch (\Exception $e) {
-            throw new RuntimeException('Cannot transform value to string!');
-        }
+        $value = (string) $value;
+
         return $value;
     }
 
@@ -436,7 +433,9 @@ class Utils
             } else {
                 $bn = new BigNumber($number);
             }
-        } elseif (!$number instanceof BigNumber){
+        } elseif ($number instanceof BigNumber){
+            $bn = $number;
+        } else {
             throw new InvalidArgumentException('toBn number must be BigNumber, string or int.');
         }
         return $bn;

test/unit/UtilsTest.php

@@ -3,6 +3,7 @@
 namespace Test\Unit;
 
 use InvalidArgumentException;
+use stdClass;
 use Test\TestCase;
 use phpseclib\Math\BigInteger as BigNumber;
 use Web3\Utils;
@@ -410,19 +411,21 @@ class UtilsTest extends TestCase
     public function testToBn()
     {
         $bn = Utils::toBn(11);
-
         $this->assertEquals($bn->toString(), '11');
 
         $bn = Utils::toBn('0x12');
-
         $this->assertEquals($bn->toString(), '18');
 
         $bn = Utils::toBn(0x12);
-
         $this->assertEquals($bn->toString(), '18');
 
         $bn = Utils::toBn('ae');
-
         $this->assertEquals($bn->toString(), '174');
+
+        $bn = Utils::toBn(new BigNumber(1));
+        $this->assertEquals($bn->toString(), '1');
+
+        $this->expectException(InvalidArgumentException::class);
+        $bn = Utils::toBn(new stdClass);
     }
 }