Buggy python submission (verdict: Runtime Error):
import java.io.PrintWriter;
import java.util.*;


public class Main {
    public static void main(String[] args) {
        PrintWriter out = new PrintWriter(System.out);
        Scanner sc = new Scanner(System.in);
        Task task = new Task();
        task.solve(sc, out);
        out.flush();
        sc.close();
    }

    static class Task {
        public void solve(Scanner sc, PrintWriter out) {
            int H = nint(sc);
            int W = nint(sc);
            List<Map<Integer, Integer>> graph = new ArrayList<>();
            List<String> sList = getStringList(sc, H);
            for (int i = 0; i <= H; i++) {
                for (int j = 0; j <= W; j++) {
                    Map<Integer, Integer> tmp = new HashMap<>();
                    graph.add(i*j, tmp);
                }
            }
            for (int i = 0; i < H; i++) {
                for (int j = 0; j < W; j++) {
                    if (sList.get(i).charAt(j) == '#') {
                        continue;
                    }
                    if (i + 1 < H && sList.get(i + 1).charAt(j) == '.') {
                        Map<Integer, Integer> tmp1 = graph.get(i * W + j);
                        tmp1.put((i + 1) * W + j, 1);
                        graph.set(i * W + j, tmp1);
                    }
                    if (j + 1 < W && sList.get(i).charAt(j + 1) == '.') {
                        Map<Integer, Integer> tmp2 = graph.get(i * W + j);
                        tmp2.put(i * W + j + 1, 1);
                        graph.set(i * W + j, tmp2);

                    }
                }
            }
            Dijkstra dijkstra = new Dijkstra(graph, 0, H*W-1);
            dijkstra.execute();
            out.println(dijkstra.getRouteCount() % 1000000007);


        }
    }

    public static class Dijkstra {
        private int startPoint;
        private int goalPoint;
        private List<Map<Integer, Integer>> routeMap;
        private int[] routeCount;
        private int[] prev;


        Dijkstra(List<Map<Integer, Integer>> routeMap, int startPoint) {
            this.startPoint = startPoint;
            this.routeMap = routeMap;
            this.goalPoint = -1;

        }

        Dijkstra(List<Map<Integer, Integer>> routeMap, int startPoint, int goalPoint) {
            this.startPoint = startPoint;
            this.routeMap = routeMap;
            this.goalPoint = goalPoint;

        }

        private int getRouteCount() {
            return this.routeCount[this.goalPoint];
        }

        public List<Integer> getPath() {
            List<Integer> path = new ArrayList<>();
            int dest = this.goalPoint;
            path.add(this.goalPoint);
            while (this.prev[dest] != Integer.MAX_VALUE) {
                path.add(prev[dest]);
                dest = prev[dest];
            }
            Collections.reverse(path);
            return path;
        }

        public int[] execute() {
            int numberOfCity = this.routeMap.size();
            int[] dist = new int[numberOfCity];
            this.prev = new int[numberOfCity];
            this.routeCount = new int[numberOfCity];
            for (int i = 0; i < numberOfCity; i++) {
                dist[i] = Integer.MAX_VALUE;
                this.prev[i] = Integer.MAX_VALUE;
                this.routeCount[i] = 0;
            }
            dist[this.startPoint] = 0;
            this.routeCount[this.startPoint] = 1;
            PriorityQueue<Node> pQueue = new PriorityQueue<>();
            pQueue.offer(new Node(this.startPoint, 0));
            while (!pQueue.isEmpty()) {
                Node node = pQueue.poll();
                int prev_cost = node.getCost();
                int src = node.getNode();
                if (dist[src] < prev_cost) {
                    continue;
                }
                for (Map.Entry<Integer, Integer> e : this.routeMap.get(src).entrySet()) {
                    int dest = e.getKey();
                    int cost = e.getValue();

                    if (cost != Integer.MAX_VALUE && dist[dest] > dist[src] + cost) {
                        dist[dest] = dist[src] + cost;
                        this.prev[dest] = src;
                        pQueue.offer(new Node(dest, dist[dest]));
                    }

                    if (dist[dest] == dist[src] + cost) {
                        this.routeCount[dest] += this.routeCount[src] % 1000000007;
                    }

                }
            }

            return dist;

        }

        class Node implements Comparable<Node> {
            private int node;
            private int cost;

            public Node(int node, int cost) {
                this.node = node;
                this.cost = cost;
            }

            @Override
            public int compareTo(Node node2) {
                return Integer.compare(this.cost, node2.cost);
            }

            public int getNode() {
                return this.node;
            }

            public int getCost() {
                return this.cost;
            }
        }

    }


    static int nint(Scanner sc) {


        return Integer.parseInt(sc.next());
    }

    static long nlong(Scanner sc) {
        return Long.parseLong(sc.next());
    }

    static double ndouble(Scanner sc) {
        return Double.parseDouble(sc.next());
    }

    static float nfloat(Scanner sc) {
        return Float.parseFloat(sc.next());
    }

    static String nstr(Scanner sc) {
        return sc.next();
    }

    static long[] longLine(Scanner sc, int size) {
        long[] lLine = new long[size];
        for (int i = 0; i < size; i++) {
            lLine[i] = nlong(sc);
        }
        return lLine;
    }

    static int[] intLine(Scanner sc, int size) {
        int[] iLine = new int[size];
        for (int i = 0; i < size; i++) {
            iLine[i] = nint(sc);
        }
        return iLine;
    }

    static String[] strLine(Scanner sc, int size) {
        String[] strLine = new String[size];
        for (int i = 0; i < size; i++) {
            strLine[i] = nstr(sc);
        }
        return strLine;
    }

    static long maxFromList(List<Long> longList) {
        return longList.stream().max(Comparator.naturalOrder()).get();
    }

    static long minFromList(List<Long> longList) {
        return longList.stream().min(Comparator.naturalOrder()).get();
    }

    public static int sumDigits(int n) {
        int sum = 0;
        while (n != 0) {
            sum += n % 10;
            n /= 10;
        }
        return sum;
    }

    public static long sumDigits(long n) {
        long sum = 0;
        while (n != 0) {
            sum += n % 10;
            n /= 10;
        }
        return sum;
    }

    static List<Integer> getIntegerList(Scanner sc, int size) {
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i < size; i++) {
            list.add(nint(sc));
        }
        return list;
    }

    static List<Long> getLongList(Scanner sc, int size) {
        List<Long> list = new ArrayList<>();
        for (int i = 0; i < size; i++) {
            list.add(nlong(sc));
        }
        return list;
    }

    static List<String> getStringList(Scanner sc, int size) {
        List<String> stringList = new ArrayList<>();
        for (int i = 0; i < size; i++) {
            stringList.add(nstr(sc));
        }
        return stringList;
    }

    private static long lcm(long a, long b) {
        return a * b / gcd(b, a % b);
    }

    private static long gcd(long a, long b) {
        return b == 0 ? a : gcd(b, a % b);
    }

    private static Map<Integer, Integer> primeFactorize(long num) {
        Map<Integer, Integer> map = new HashMap<>();
        int i = 2;
        while (i * i <= num) {
            while (num % i == 0) {
                num /= i;
                if (map.containsKey(i)) {
                    int tmp = map.get(i);
                    tmp++;
                    map.put(i, tmp);
                } else {
                    map.put(i, 1);
                }
            }
            i++;
        }
        if (num > 1)
            map.put((int) num, 1);
        return map;
    }

    /**
     * Returns the most frequent value in the list. リスト内で最頻出数値を返します。
     *
     * @param list List
     * @return most frequent value
     */
    private static Integer getMode(List<Integer> list) {
        if (list.size() <= 0) {
            throw new IllegalArgumentException();
        }

        Map<Integer, Integer> modeMap = new HashMap<>();

        for (Integer x : list) {
            if (modeMap.containsKey(x)) {
                modeMap.put(x, modeMap.get(x) + 1);
            } else {
                modeMap.put(x, 1);
            }
        }
        return modeMap.entrySet().stream()
                .max(Map.Entry.comparingByValue())
                .get()
                .getKey();

    }
}



Fixed submission:
H, W = map(int, input().split())
s_list = []
for i in range(H):
    s = list(input())
    s_list.append(s)

dp = [[0 for _ in range(W)] for _ in range(H)]
dp[0][0] = 1
mod = 10 ** 9 + 7
for i in range(H):
    for j in range(W):
        if s_list[i][j] == "#":
            continue
        if i + 1 < H and s_list[i + 1][j] == ".":
            dp[i + 1][j] += dp[i][j] % mod
        if j + 1 < W and s_list[i][j + 1] == ".":
            dp[i][j + 1] += dp[i][j] % mod
print(dp[H - 1][W - 1] % mod)

Buggy python submission (verdict: Time Limit Exceeded):
import heapq


class Dijkstra:

    def __init__(self, rote_map, start_point, goal_point=None):
        self.rote_map = rote_map
        self.start_point = start_point
        self.goal_point = goal_point

    def execute(self):
        num_of_city = len(self.rote_map)
        dist = [float("inf") for _ in range(num_of_city)]
        prev = [float("inf") for _ in range(num_of_city)]

        dist[self.start_point] = 0
        heap_q = []
        heapq.heappush(heap_q, (0, self.start_point))
        route_count = [0 for _ in range(num_of_city)]
        route_count[self.start_point] = 1
        while len(heap_q) != 0:
            prev_cost, src = heapq.heappop(heap_q)

            if dist[src] < prev_cost:
                continue

            for dest, cost in self.rote_map[src].items():
                if cost != float("inf") and dist[dest] > dist[src] + cost:
                    dist[dest] = dist[src] + cost
                    heapq.heappush(heap_q, (dist[dest], dest))
                    prev[dest] = src
                if dist[dest] == dist[src] + cost:
                    route_count[dest] += route_count[src]

        if self.goal_point is not None:
            return self._get_path(self.goal_point, prev)
        else:
            return dist, route_count

    def _get_path(self, goal, prev):
        path = [goal]
        dest = goal

        while prev[dest] != float("inf"):
            path.append(prev[dest])
            dest = prev[dest]

        return list(reversed(path))


H, W = map(int, input().split())
graph = [dict() for _ in range(H * W)]
s_list = []
for i in range(H):
    s = list(input())
    s_list.append(s)

for i in range(H):
    for j in range(W):
        if s_list[i][j] == "#":
            continue
        if i + 1 < H and s_list[i + 1][j] == ".":
            graph[i * W + j][(i + 1) * W + j] = 1

        if j + 1 < W and s_list[i][j + 1] == ".":
            graph[i * W + j][i * W + j + 1] = 1

dijkstra = Dijkstra(graph, 0)
_, dijkstra_result = dijkstra.execute()

print(dijkstra_result[-1] % (10**9 + 7))


Fixed submission:
H, W = map(int, input().split())
s_list = []
for i in range(H):
    s = list(input())
    s_list.append(s)

dp = [[0 for _ in range(W)] for _ in range(H)]
dp[0][0] = 1
mod = 10 ** 9 + 7
for i in range(H):
    for j in range(W):
        if s_list[i][j] == "#":
            continue
        if i + 1 < H and s_list[i + 1][j] == ".":
            dp[i + 1][j] += dp[i][j] % mod
        if j + 1 < W and s_list[i][j + 1] == ".":
            dp[i][j + 1] += dp[i][j] % mod
print(dp[H - 1][W - 1] % mod)