Fix missing file error with sage_getdoc

Author: user202729

src/sage/misc/sageinspect.py

@@ -2156,6 +2156,8 @@ def sage_getdoc(obj, obj_name='', embedded=False):
     The optional boolean argument ``embedded`` controls the
     string formatting. It is False by default.
 
+    Return ``None`` if the documentation string is invalid or missing.
+
     INPUT:
 
     - ``obj`` -- a function, module, etc.: something with a docstring
@@ -2166,7 +2168,8 @@ def sage_getdoc(obj, obj_name='', embedded=False):
         sage: sage_getdoc(identity_matrix)[87:124]                                      # needs sage.modules
         '...the n x n identity matrix...'
         sage: def f(a, b, c, d=1): return a+b+c+d
-        ...
+        sage: sage_getdoc(f) is None
+        True
         sage: import functools
         sage: f1 = functools.partial(f, 1,c=2)
         sage: f.__doc__ = "original documentation"
@@ -2175,13 +2178,25 @@ def sage_getdoc(obj, obj_name='', embedded=False):
         'original documentation\n'
         sage: sage_getdoc(f1)
         'specialised documentation\n'
+
+    TESTS::
+
+        sage: class C:
+        ....:     '''
+        ....:     docs
+        ....:     '''
+        sage: sage_getdoc(C)
+        '   docs\n'
     """
     import sage.misc.sagedoc
     if obj is None:
         return ''
     r = sage_getdoc_original(obj)
     s = sage.misc.sagedoc.format(r, embedded=embedded)
-    f = sage_getfile(obj)
+    try:
+        f = sage_getfile(obj)
+    except OSError:
+        f = None
     if f and os.path.exists(f):
         from sage.doctest.control import skipfile
         skip = skipfile(f)