rtabmap: free space behind the walls

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I am running rtabmap in gazebo with turtlebot3 without lidar, only with camera. here is my rtabmap parameters: <group ns="rtabmap">

<node name="rtabmap" pkg="rtabmap_ros" type="rtabmap" output="screen" args="$(arg rtabmap_args)">

  <param name="database_path"       type="string" value="$(arg database_path)"/>
  <param name="frame_id"            type="string" value="base_footprint"/>
  <param name="subscribe_depth"     type="bool"   value="true"/>
  <param name="subscribe_rgbd"      type="bool"   value="false"/>
  <param name="subscribe_scan"      type="bool"   value="false"/>

  <!-- Input topics -->
  <remap from="scan"                to="$(arg input_scan)"/>
  <remap from="odom"                to="$(arg input_odom)"/>
  <remap from="rgb/image"           to="$(arg input_image)"/>
  <remap from="depth/image"         to="$(arg input_depth)"/>
  <remap from="rgb/camera_info"     to="$(arg input_camera_info)"/>
  <remap from="rgbd_image"          to="rgbd_image"/>

  <!-- Output topics -->
  <remap from="grid_map" to="/map"/>

  <param name="queue_size" type="int" value="100"/>

  <!-- RTAB-Map's parameters -->
  <param name="RGBD/NeighborLinkRefining" type="string" value="false"/>
  <param name="RGBD/ProximityBySpace"     type="string" value="true"/>
  <param name="RGBD/OptimizeFromGraphEnd" type="string" value="false"/>
  <param name="RGBD/AngularUpdate"        type="string" value="0.05"/>
  <param name="RGBD/LinearUpdate"         type="string" value="0.05"/>
  <param name="Optimizer/GravitySigma"    type="string" value="0.1"/>
  <!--param name="Optimizer/Slam2D"          type="string" value="true"/-->
  <param name="Reg/Force3DoF"             type="string" value="true"/>
  <param name="Reg/Strategy"              type="string" value="0"/> <!-- 1=ICP -->
  <param name="Vis/MinInliers"            type="string" value="20"/>
  <param name="Vis/InlierDistance"        type="string" value="0.1"/>
  <param name="Kp/MaxDepth"               type="string" value="0"/>
  <param name="Vis/MaxDepth"              type="string" value="0"/>
  <param name="Rtabmap/TimeThr"           type="string" value="0"/>
  <param name="Rtabmap/DetectionRate"     type="string" value="$(arg rate)" />
  <param name="Mem/RehearsalSimilarity"   type="string" value="0.45"/>
  <param name="Mem/UseOdomGravity=true"   type="string" value="true"/>
  <param name="Grid/MaxObstacleHeight"    type="string" value="0.75" />
  <param name="Grid/NoiseFilteringRadius" type="string" value="0.0"/>
  <param name="Grid/NoiseFilteringMinNeighbors" type="string" value="5.0"/>

  <param name="Grid/FromDepth"            type="bool" value="true" />
  <!--param name="Grid/DepthDecimation"      type="string" value="10"/-->
  <param name="Grid/3D"                   type="bool" value="true" />
  <param name="Grid/RayTracing"           type="bool" value="true" />
  <param name="Grid/NormalsSegmentation"  type="string" value="true" />
  <param name="Grid/MaxGroundHeight"      type="string" value="0.03" />
  <param name="Grid/RangeMax"             type="string" value="5.0" />
  <param name="Grid/FlatObstacleDetected" type="bool" value="true"/>     


  <param name="Icp/VoxelSize"             type="string" value="0.05"/>
  <param name="Icp/MaxCorrespondenceDistance"            type="string" value="0.1"/>

  <!-- Localization mode -->
  <param     if="$(arg localization)" name="Mem/IncrementalMemory" type="string" value="false"/>
  <param unless="$(arg localization)" name="Mem/IncrementalMemory" type="string" value="true"/>
  <param name="Mem/InitWMWithAllNodes" type="string" value="$(arg localization)"/>

</node>

</group>

I have problem that map is exploring with free space behind the walls (marked with red):

Space that camera cannot see ... (more)