Make IF/ELSE statements more concise by using MERGE

src/FileType_HDF5.f90

@@ -7224,11 +7224,7 @@ SUBROUTINE write_attribute_b0(this,obj_name,attr_name,attr_val)
   CALL h5screate_simple_f(num_dims,dims,dspace_id,error)
 
   !Create and write to the attribute within the dataspce
-  IF(attr_val) THEN
-    char_attr_val='T'
-  ELSE
-    char_attr_val='F'
-  ENDIF
+char_attr_val = MERGE('T','F',attr_val)
   CALL createAttribute(this,obj_id,attr_name,H5T_NATIVE_CHARACTER,&
       dspace_id,attr_id)
   CALL h5awrite_f(attr_id,H5T_NATIVE_CHARACTER,char_attr_val,dims,error)