diagnostic.py: Check row and column number

Row and column number should be zero-based integer, not null

Fixes #37

coala_langserver/diagnostic.py

@@ -15,17 +15,33 @@ def output_to_diagnostics(output):
             origin = problem['origin']
             real_message = '[{}] {}: {}'.format(section, origin, message)
             for code in problem['affected_code']:
+                """
+                Line position and character offset should be zero-based
+                according to LSP, but row number of coala is one-based.
+                Line position and character offset should be numbers.
+                """
+                start_line = code['start']['line'] - 1
+                start_char = code['start']['column']
+                end_line = code['end']['line'] - 1
+                end_char = code['end']['column']
+                if start_line is None:
+                    start_line = 0
+                if start_char is None:
+                    start_char = 0
+                if end_line is None:
+                    end_line = 0
+                if end_char is None:
+                    end_char = 0
                 res.append({
                     'severity': severity,
                     'range': {
                         'start': {
-                            # Trick: VS Code starts from 0?
-                            'line': code['start']['line'] - 1,
-                            'character': code['start']['column']
+                            'line': start_line,
+                            'character': start_char
                         },
                         'end': {
-                            'line': code['end']['line'] - 1,
-                            'character': code['end']['column']
+                            'line': end_line,
+                            'character': end_char
                         }
                     },
                     'source': 'coala',