Remove redundant constant nil argument to gethash

* lisp/cedet/ede/files.el (ede--directory-project-from-hash):
* lisp/emacs-lisp/edebug.el (edebug-unwrap*):
* lisp/emacs-lisp/testcover.el (testcover--copy-object1):
* lisp/net/zeroconf.el (zeroconf-get-service, zeroconf-resolve-service)
(zeroconf-register-service-browser, zeroconf-service-browser-handler)
(zeroconf-register-service-resolver):
* lisp/url/url-history.el (url-have-visited-url): Remove redundant
constant nil argument to gethash.

lisp/cedet/ede/files.el

@@ -282,7 +282,7 @@ Do this whenever a new project is created, as opposed to loaded."
 (defun ede--directory-project-from-hash (dir)
   "If there is an already loaded project for DIR, return it from the hash."
   (setq dir (expand-file-name dir))
-  (gethash dir ede-project-directory-hash nil))
+  (gethash dir ede-project-directory-hash))
 
 (defun ede--directory-project-add-description-to-hash (dir desc)
   "Add to the EDE project hash DIR associated with DESC."

lisp/emacs-lisp/edebug.el

@@ -1288,7 +1288,7 @@ infinite loops when the code/environment contains a circular object.")
   (while (not (eq sexp (setq sexp (edebug-unwrap sexp)))))
   (cond
    ((consp sexp)
-    (or (gethash sexp edebug--unwrap-cache nil)
+    (or (gethash sexp edebug--unwrap-cache)
 	(let ((remainder sexp)
 	      (current (cons nil nil)))
 	  (prog1 current
@@ -1303,8 +1303,8 @@ infinite loops when the code/environment contains a circular object.")
 		    (setf (cdr current)
 			  (edebug-unwrap* remainder))
 		    nil)
-		   ((gethash remainder edebug--unwrap-cache nil)
-		    (setf (cdr current) (gethash remainder edebug--unwrap-cache nil))
+                   ((gethash remainder edebug--unwrap-cache)
+                    (setf (cdr current) (gethash remainder edebug--unwrap-cache))
 		    nil)
 		   (t (setq current
 			    (setf (cdr current) (cons nil nil)))))))))))

lisp/emacs-lisp/testcover.el

@@ -296,7 +296,7 @@ iteratively copies its cdr.  When VECP is non-nil, copy
 vectors as well as conses."
   (if (and (atom obj) (or (not vecp) (not (vectorp obj))))
       obj
-    (let ((copy (gethash obj hash-table nil)))
+    (let ((copy (gethash obj hash-table)))
       (unless copy
         (cond
          ((consp obj)
@@ -315,7 +315,7 @@ vectors as well as conses."
                           (testcover--copy-object1 rest vecp hash-table))
                     nil)
                    ((gethash rest hash-table nil)
-                    (setf (cdr current) (gethash rest hash-table nil))
+                    (setf (cdr current) (gethash rest hash-table))
                     nil)
                    (t (setq current
                             (setf (cdr current) (cons nil nil)))))))))

lisp/net/zeroconf.el

@@ -380,7 +380,7 @@ TYPE.  The resulting list has the format
   (INTERFACE PROTOCOL NAME TYPE DOMAIN FLAGS)."
   ;; Due to the service browser, all known services are kept in
   ;; `zeroconf-services-hash'.
-  (gethash (concat name "/" type) zeroconf-services-hash nil))
+  (gethash (concat name "/" type) zeroconf-services-hash))
 
 (defvar dbus-debug)
 
@@ -396,7 +396,7 @@ TYPE.  The resulting list has the format
 
     (or
      ;; Check whether we know this service already.
-     (gethash key zeroconf-resolved-services-hash nil)
+     (gethash key zeroconf-resolved-services-hash)
 
      ;; Resolve the service.  We don't propagate D-Bus errors.
      (dbus-ignore-errors
@@ -552,7 +552,7 @@ DOMAIN is nil, the local domain is used."
 
 (defun zeroconf-register-service-browser (type)
   "Register a service browser at the Avahi daemon."
-  (or (gethash type zeroconf-path-avahi-service-browser-hash nil)
+  (or (gethash type zeroconf-path-avahi-service-browser-hash)
       (puthash type
 	       (dbus-call-method
 		:system zeroconf-service-avahi zeroconf-path-avahi
@@ -573,8 +573,8 @@ DOMAIN is nil, the local domain is used."
   (let* ((name (zeroconf-service-name val))
 	 (type (zeroconf-service-type val))
 	 (key (concat name "/" type))
-	 (ahook (gethash type zeroconf-service-added-hooks-hash nil))
-	 (rhook (gethash type zeroconf-service-removed-hooks-hash nil)))
+         (ahook (gethash type zeroconf-service-added-hooks-hash))
+         (rhook (gethash type zeroconf-service-removed-hooks-hash)))
     (cond
      ((string-equal (dbus-event-member-name last-input-event) "ItemNew")
       ;; Add new service.
@@ -590,7 +590,7 @@ DOMAIN is nil, the local domain is used."
 (defun zeroconf-register-service-resolver (name type)
   "Register a service resolver at the Avahi daemon."
   (let ((key (concat name "/" type)))
-    (or (gethash key zeroconf-path-avahi-service-resolver-hash nil)
+    (or (gethash key zeroconf-path-avahi-service-resolver-hash)
 	(puthash key
 		 (dbus-call-method
 		  :system zeroconf-service-avahi zeroconf-path-avahi

lisp/url/url-history.el

@@ -154,7 +154,7 @@ user for what type to save as."
 
 (defun url-have-visited-url (url)
   (url-do-setup)
-  (gethash url url-history-hash-table nil))
+  (gethash url url-history-hash-table))
 
 (defun url-completion-function (string predicate function)
   (declare (obsolete url-history-hash-table "26.1"))