Patch against 1.7.18:

[[[
Index: subversion/mod_dav_svn/reports/deleted-rev.c
===================================================================
--- subversion/mod_dav_svn/reports/deleted-rev.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/deleted-rev.c	(working copy)
@@ -56,6 +56,9 @@ dav_svn__get_deleted_rev_report(const dav_resource
   dav_error *derr = NULL;
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   if (ns == -1)
     return dav_svn__new_error_tag(resource->pool, HTTP_BAD_REQUEST, 0,
Index: subversion/mod_dav_svn/reports/file-revs.c
===================================================================
--- subversion/mod_dav_svn/reports/file-revs.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/file-revs.c	(working copy)
@@ -251,6 +251,9 @@ dav_svn__file_revs_report(const dav_resource *reso
   arb.repos = resource->info->repos;
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   /* ### This is done on other places, but the document element is
      in this namespace, so is this necessary at all? */
Index: subversion/mod_dav_svn/reports/get-location-segments.c
===================================================================
--- subversion/mod_dav_svn/reports/get-location-segments.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/get-location-segments.c	(working copy)
@@ -123,6 +123,9 @@ dav_svn__get_location_segments_report(const dav_re
   struct location_segment_baton location_segment_baton;
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   if (ns == -1)
     {
Index: subversion/mod_dav_svn/reports/get-locations.c
===================================================================
--- subversion/mod_dav_svn/reports/get-locations.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/get-locations.c	(working copy)
@@ -106,6 +106,9 @@ dav_svn__get_locations_report(const dav_resource *
                                       sizeof(svn_revnum_t));
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   if (ns == -1)
     {
Index: subversion/mod_dav_svn/reports/log.c
===================================================================
--- subversion/mod_dav_svn/reports/log.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/log.c	(working copy)
@@ -307,6 +307,9 @@ dav_svn__log_report(const dav_resource *resource,
     = apr_array_make(resource->pool, 1, sizeof(const char *));
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   if (ns == -1)
     {
Index: subversion/mod_dav_svn/reports/mergeinfo.c
===================================================================
--- subversion/mod_dav_svn/reports/mergeinfo.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/mergeinfo.c	(working copy)
@@ -67,6 +67,9 @@ dav_svn__get_mergeinfo_report(const dav_resource *
     = apr_array_make(resource->pool, 0, sizeof(const char *));
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   if (ns == -1)
     {
]]]

  Patch against 1.8.10:

[[[
Index: subversion/mod_dav_svn/reports/deleted-rev.c
===================================================================
--- subversion/mod_dav_svn/reports/deleted-rev.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/deleted-rev.c	(working copy)
@@ -56,6 +56,9 @@ dav_svn__get_deleted_rev_report(const dav_resource
   dav_error *derr = NULL;
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   if (ns == -1)
     return dav_svn__new_error_tag(resource->pool, HTTP_BAD_REQUEST, 0,
Index: subversion/mod_dav_svn/reports/file-revs.c
===================================================================
--- subversion/mod_dav_svn/reports/file-revs.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/file-revs.c	(working copy)
@@ -254,6 +254,9 @@ dav_svn__file_revs_report(const dav_resource *reso
   arb.repos = resource->info->repos;
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   /* ### This is done on other places, but the document element is
      in this namespace, so is this necessary at all? */
Index: subversion/mod_dav_svn/reports/get-location-segments.c
===================================================================
--- subversion/mod_dav_svn/reports/get-location-segments.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/get-location-segments.c	(working copy)
@@ -123,6 +123,9 @@ dav_svn__get_location_segments_report(const dav_re
   struct location_segment_baton location_segment_baton;
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   if (ns == -1)
     {
Index: subversion/mod_dav_svn/reports/get-locations.c
===================================================================
--- subversion/mod_dav_svn/reports/get-locations.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/get-locations.c	(working copy)
@@ -106,6 +106,9 @@ dav_svn__get_locations_report(const dav_resource *
                                       sizeof(svn_revnum_t));
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   if (ns == -1)
     {
Index: subversion/mod_dav_svn/reports/inherited-props.c
===================================================================
--- subversion/mod_dav_svn/reports/inherited-props.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/inherited-props.c	(working copy)
@@ -63,6 +63,9 @@ dav_svn__get_inherited_props_report(const dav_reso
   apr_pool_t *iterpool;
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   if (ns == -1)
     {
Index: subversion/mod_dav_svn/reports/log.c
===================================================================
--- subversion/mod_dav_svn/reports/log.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/log.c	(working copy)
@@ -307,6 +307,9 @@ dav_svn__log_report(const dav_resource *resource,
     = apr_array_make(resource->pool, 1, sizeof(const char *));
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   if (ns == -1)
     {
Index: subversion/mod_dav_svn/reports/mergeinfo.c
===================================================================
--- subversion/mod_dav_svn/reports/mergeinfo.c	(revision 1624477)
+++ subversion/mod_dav_svn/reports/mergeinfo.c	(working copy)
@@ -67,6 +67,9 @@ dav_svn__get_mergeinfo_report(const dav_resource *
     = apr_array_make(resource->pool, 0, sizeof(const char *));
 
   /* Sanity check. */
+  if (!resource->info->repos_path)
+    return dav_svn__new_error(resource->pool, HTTP_BAD_REQUEST, 0,
+                              "The request does not specify a repository path");
   ns = dav_svn__find_ns(doc->namespaces, SVN_XML_NAMESPACE);
   if (ns == -1)
     {
]]]