improve error messages

Author: joonlabs

src/Execution/Executor.php

@@ -367,7 +367,7 @@ function completeValue(ExecutionContext $executionContext, GraphQLType $returnTy
             );
             if ($completed === null) {
                 throw new GraphQLError(
-                    "Cannot return null for non-nullable field {$info["parentType"]->getName()}.{$info["fieldName"]}."
+                    "Cannot use [null] for non-nullable field {$info["parentType"]->getName()}.{$info["fieldName"]}."
                 );
             }
             return $completed;

src/Parser/Parser.php

@@ -824,7 +824,7 @@ private function eat(string $tokenType)
         }
         if ($token["type"] !== $tokenType) {
             throw new UnexpectedTokenError(
-                "Unexpected token: \"" . $token["value"] . "\", expected token of type \"$tokenType\", got tyoe \"" . $token["type"] . "\".",
+                "Unexpected token: \"" . $token["value"] . "\", expected token of type \"$tokenType\", got type \"" . $token["type"] . "\".",
                 $this->tokenizer->getLastLocation()
             );
         }