8329099: Undocumented exception thrown by Instruction factory methods accepting Opcode

Reviewed-by: briangoetz

src/java.base/share/classes/java/lang/classfile/package-info.java

@@ -238,6 +238,12 @@
  * the convenience method {@code CodeBuilder.invokeInstruction}, which in turn behaves
  * as if it calls method {@code CodeBuilder.with}. This composing of method calls on the
  * builder enables the composing of transforms (as described later).
+ * <p>
+ * Unless otherwise noted, passing a {@code null} argument to a constructor
+ * or method of any Class-File API class or interface will cause a {@link
+ * java.lang.NullPointerException NullPointerException} to be thrown. Additionally,
+ * invoking a method with an array or collection containing a {@code null} element
+ * will cause a {@code NullPointerException}, unless otherwise specified. </p>
  *
  * <h3>Symbolic information</h3>
  * To describe symbolic information for classes and types, the API uses the