Fix error in selective restore when only one user database exists in the cluster.

Fixed by Cynthia Shang.
Reported by Nj Baliyan.

doc/xml/release.xml

@@ -14,6 +14,17 @@
     <release-list>
         <release date="XXXX-XX-XX" version="2.04dev" title="UNDER DEVELOPMENT">
             <release-core-list>
+                <release-bug-list>
+                    <release-item>
+                        <release-item-contributor-list>
+                            <release-item-ideator id="nj.baliyan"/>
+                            <release-item-contributor id="shang.cynthia"/>
+                        </release-item-contributor-list>
+
+                        <p>Fix error in selective restore when only one user database exists in the cluster.</p>
+                    </release-item>
+                </release-bug-list>
+
                 <release-feature-list>
                     <release-item>
                         <p><postgres/> 11 Beta 1 support.</p>
@@ -4775,6 +4786,11 @@
             <contributor-id type="github">bradnicholson</contributor-id>
         </contributor>
 
+        <contributor id="nj.baliyan">
+            <contributor-name-display>Nj Baliyan</contributor-name-display>
+            <contributor-id type="github">nj3110</contributor-id>
+        </contributor>
+
         <contributor id="nullmeier.markus">
             <contributor-name-display>Markus Nullmeier</contributor-name-display>
             <contributor-id type="github">mnullmei</contributor-id>

lib/pgBackRest/Restore.pm

@@ -1221,7 +1221,7 @@ sub process
         }
 
         # Output the generated filter for debugging
-        &log(DETAIL, "database filter: $strDbFilter");
+        &log(DETAIL, "database filter: " . (defined($strDbFilter) ? "${strDbFilter}" : ''));
     }
 
     # Initialize the restore process

src/perl/embed.auto.c

@@ -19204,7 +19204,7 @@ static const EmbeddedModule embeddedModule[] =
             "}\n"
             "\n"
             "\n"
-            "&log(DETAIL, \"database filter: $strDbFilter\");\n"
+            "&log(DETAIL, \"database filter: \" . (defined($strDbFilter) ? \"${strDbFilter}\" : ''));\n"
             "}\n"
             "\n"
             "\n"