Clarify documentation about PASSWORD in CREATE/ALTER ROLE

The documentation of CREATE/ALTER ROLE has been missing two things
related to PASSWORD:
- The password value provided needs to be quoted, some places of the
documentation marked the field with quotes, but not others, which led to
confusion.
- PASSWORD NULL was not provided consistently, with ENCRYPTED being not
compatible with it.

Reported-by: Steven Winfield
Author: Michael Paquier
Reviewed-by: David G. Johnston
Discussion: https://postgr.es/m/154282901979.1316.7418475422120496802@wrigleys.postgresql.org

doc/src/sgml/ref/alter_role.sgml

@@ -33,7 +33,7 @@ ALTER ROLE <replaceable class="parameter">role_specification</replaceable> [ WIT
     | REPLICATION | NOREPLICATION
     | BYPASSRLS | NOBYPASSRLS
     | CONNECTION LIMIT <replaceable class="parameter">connlimit</replaceable>
-    | [ ENCRYPTED ] PASSWORD '<replaceable class="parameter">password</replaceable>'
+    | [ ENCRYPTED ] PASSWORD '<replaceable class="parameter">password</replaceable>' | PASSWORD NULL
     | VALID UNTIL '<replaceable class="parameter">timestamp</replaceable>'
 
 ALTER ROLE <replaceable class="parameter">name</replaceable> RENAME TO <replaceable>new_name</replaceable>
@@ -168,7 +168,8 @@ ALTER ROLE { <replaceable class="parameter">role_specification</replaceable> | A
       <term><literal>BYPASSRLS</literal></term>
       <term><literal>NOBYPASSRLS</literal></term>
       <term><literal>CONNECTION LIMIT</literal> <replaceable class="parameter">connlimit</replaceable></term>
-      <term>[ <literal>ENCRYPTED</literal> ] <literal>PASSWORD</literal> <replaceable class="parameter">password</replaceable></term>
+      <term>[ <literal>ENCRYPTED</literal> ] <literal>PASSWORD</literal> '<replaceable class="parameter">password</replaceable>'</term>
+      <term><literal>PASSWORD NULL</literal></term>
       <term><literal>VALID UNTIL</literal> '<replaceable class="parameter">timestamp</replaceable>'</term>
       <listitem>
        <para>

doc/src/sgml/ref/alter_user.sgml

@@ -33,7 +33,7 @@ ALTER USER <replaceable class="parameter">role_specification</replaceable> [ WIT
     | REPLICATION | NOREPLICATION
     | BYPASSRLS | NOBYPASSRLS
     | CONNECTION LIMIT <replaceable class="parameter">connlimit</replaceable>
-    | [ ENCRYPTED ] PASSWORD '<replaceable class="parameter">password</replaceable>'
+    | [ ENCRYPTED ] PASSWORD '<replaceable class="parameter">password</replaceable>' | PASSWORD NULL
     | VALID UNTIL '<replaceable class="parameter">timestamp</replaceable>'
 
 ALTER USER <replaceable class="parameter">name</replaceable> RENAME TO <replaceable>new_name</replaceable>

doc/src/sgml/ref/create_role.sgml

@@ -33,7 +33,7 @@ CREATE ROLE <replaceable class="parameter">name</replaceable> [ [ WITH ] <replac
     | REPLICATION | NOREPLICATION
     | BYPASSRLS | NOBYPASSRLS
     | CONNECTION LIMIT <replaceable class="parameter">connlimit</replaceable>
-    | [ ENCRYPTED ] PASSWORD '<replaceable class="parameter">password</replaceable>'
+    | [ ENCRYPTED ] PASSWORD '<replaceable class="parameter">password</replaceable>' | PASSWORD NULL
     | VALID UNTIL '<replaceable class="parameter">timestamp</replaceable>'
     | IN ROLE <replaceable class="parameter">role_name</replaceable> [, ...]
     | IN GROUP <replaceable class="parameter">role_name</replaceable> [, ...]
@@ -210,7 +210,8 @@ CREATE ROLE <replaceable class="parameter">name</replaceable> [ [ WITH ] <replac
      </varlistentry>
 
      <varlistentry>
-      <term>[ <literal>ENCRYPTED</literal> ] <literal>PASSWORD</literal> <replaceable class="parameter">password</replaceable></term>
+      <term>[ <literal>ENCRYPTED</literal> ] <literal>PASSWORD</literal> '<replaceable class="parameter">password</replaceable>'</term>
+      <term><literal>PASSWORD NULL</literal></term>
       <listitem>
        <para>
         Sets the role's password.  (A password is only of use for

doc/src/sgml/ref/create_user.sgml

@@ -33,7 +33,7 @@ CREATE USER <replaceable class="parameter">name</replaceable> [ [ WITH ] <replac
     | REPLICATION | NOREPLICATION
     | BYPASSRLS | NOBYPASSRLS
     | CONNECTION LIMIT <replaceable class="parameter">connlimit</replaceable>
-    | [ ENCRYPTED ] PASSWORD '<replaceable class="parameter">password</replaceable>'
+    | [ ENCRYPTED ] PASSWORD '<replaceable class="parameter">password</replaceable>' | PASSWORD NULL
     | VALID UNTIL '<replaceable class="parameter">timestamp</replaceable>'
     | IN ROLE <replaceable class="parameter">role_name</replaceable> [, ...]
     | IN GROUP <replaceable class="parameter">role_name</replaceable> [, ...]