check with NULL

Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>

crypto/asn1/a_sign.c

@@ -243,12 +243,12 @@ int ASN1_item_sign_ctx(const ASN1_ITEM *it,
     type = EVP_MD_CTX_md(ctx);
     pkey = EVP_PKEY_CTX_get0_pkey(EVP_MD_CTX_pkey_ctx(ctx));
 
-    if (NULL == type || NULL == pkey) {
+    if (type == NULL || pkey == NULL) {
         ASN1err(ASN1_F_ASN1_ITEM_SIGN_CTX, ASN1_R_CONTEXT_NOT_INITIALISED);
         goto err;
     }
 
-    if (NULL == pkey->ameth) {
+    if (pkey->ameth == NULL) {
         ASN1err(ASN1_F_ASN1_ITEM_SIGN_CTX, ASN1_R_DIGEST_AND_KEY_TYPE_NOT_SUPPORTED);
         goto err;
     }